WIP

databuild/build_state/event_handlers.rs

@@ -340,18 +340,51 @@ impl BuildState {
     }
 
     pub(crate) fn handle_job_run_success(&mut self, event: &JobRunSuccessEventV1) -> Vec<Event> {
+        use std::collections::BTreeMap;
+
         let job_run = self.job_runs.remove(&event.job_run_id).expect(&format!(
             "BUG: Job run {} must exist when success event received",
             event.job_run_id
         ));
 
+        // Resolve read partition UUIDs from the read_deps in the event
+        let mut read_partition_uuids: BTreeMap<String, String> = BTreeMap::new();
+        for read_dep in &event.read_deps {
+            for read_ref in &read_dep.read {
+                if let Some(uuid) = self.get_canonical_partition_uuid(&read_ref.r#ref) {
+                    read_partition_uuids.insert(read_ref.r#ref.clone(), uuid.to_string());
+                }
+            }
+        }
+
+        // Get the building partitions from the job run to resolve wrote_partition_uuids
+        let building_partitions = match &job_run {
+            JobRun::Running(running) => running.info.building_partitions.clone(),
+            _ => vec![],
+        };
+
+        // Resolve wrote partition UUIDs - these will be set when we transition partitions to Live
+        // For now, we compute them based on job_run_id (same logic as transition_partitions_to_live)
+        let mut wrote_partition_uuids: BTreeMap<String, String> = BTreeMap::new();
+        for pref in &building_partitions {
+            let uuid =
+                crate::partition_state::derive_partition_uuid(&event.job_run_id, &pref.r#ref);
+            wrote_partition_uuids.insert(pref.r#ref.clone(), uuid.to_string());
+        }
+
         let succeeded = match job_run {
             JobRun::Running(running) => {
                 tracing::info!(
                     job_run_id = %event.job_run_id,
+                    read_deps_count = event.read_deps.len(),
                     "JobRun: Running → Succeeded"
                 );
-                running.succeed(current_timestamp())
+                running.succeed(
+                    current_timestamp(),
+                    event.read_deps.clone(),
+                    read_partition_uuids.clone(),
+                    wrote_partition_uuids.clone(),
+                )
             }
             _ => {
                 panic!(
@@ -361,6 +394,34 @@ impl BuildState {
             }
         };
 
+        // Populate the consumer index from read_deps (using UUIDs for historical lineage)
+        // For each read partition UUID, record that the written partition UUIDs consumed it
+        for read_dep in &event.read_deps {
+            for read_ref in &read_dep.read {
+                // Look up the read partition's UUID
+                if let Some(read_uuid) = read_partition_uuids.get(&read_ref.r#ref) {
+                    if let Ok(read_uuid) = uuid::Uuid::parse_str(read_uuid) {
+                        let consumers = self
+                            .partition_consumers
+                            .entry(read_uuid)
+                            .or_insert_with(Vec::new);
+                        for impacted_ref in &read_dep.impacted {
+                            // Look up the impacted (output) partition's UUID
+                            if let Some(wrote_uuid) = wrote_partition_uuids.get(&impacted_ref.r#ref)
+                            {
+                                if let Ok(wrote_uuid) = uuid::Uuid::parse_str(wrote_uuid) {
+                                    let entry = (wrote_uuid, event.job_run_id.clone());
+                                    if !consumers.contains(&entry) {
+                                        consumers.push(entry);
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
         // Job run success is SOURCE of truth that partitions are live
         let newly_live_partitions = succeeded.get_completed_partitions();
 
@@ -642,7 +703,6 @@ impl BuildState {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::{MissingDeps, WantAttributedPartitions};
 
     mod want {
         use super::*;
@@ -686,133 +746,25 @@ mod tests {
 
         #[test]
         fn test_multihop_dependency_replay() {
-            use crate::{
-                JobRunBufferEventV1, JobRunHeartbeatEventV1, JobRunMissingDepsEventV1,
-                JobRunSuccessEventV1, MissingDeps, PartitionRef, WantAttributedPartitions,
-                WantCreateEventV1,
-            };
+            use crate::util::test_scenarios::multihop_scenario;
 
-            let mut state = BuildState::default();
-            let mut events = vec![];
-
-            // 1. Create want for data/beta
-            let beta_want_id = "beta-want".to_string();
-            let mut create_beta = WantCreateEventV1::default();
-            create_beta.want_id = beta_want_id.clone();
-            create_beta.partitions = vec![PartitionRef {
-                r#ref: "data/beta".to_string(),
-            }];
-            events.push(Event::WantCreateV1(create_beta));
-
-            // 2. Queue beta job (first attempt)
-            let beta_job_1_id = "beta-job-1".to_string();
-            let mut buffer_beta_1 = JobRunBufferEventV1::default();
-            buffer_beta_1.job_run_id = beta_job_1_id.clone();
-            buffer_beta_1.job_label = "//job_beta".to_string();
-            buffer_beta_1.want_attributed_partitions = vec![WantAttributedPartitions {
-                want_id: beta_want_id.clone(),
-                partitions: vec![PartitionRef {
-                    r#ref: "data/beta".to_string(),
-                }],
-            }];
-            buffer_beta_1.building_partitions = vec![PartitionRef {
-                r#ref: "data/beta".to_string(),
-            }];
-            events.push(Event::JobRunBufferV1(buffer_beta_1));
-
-            // 3. Beta job starts running
-            let mut heartbeat_beta_1 = JobRunHeartbeatEventV1::default();
-            heartbeat_beta_1.job_run_id = beta_job_1_id.clone();
-            events.push(Event::JobRunHeartbeatV1(heartbeat_beta_1));
-
-            // 4. Beta job reports missing dependency on data/alpha
-            let mut dep_miss_beta_1 = JobRunMissingDepsEventV1::default();
-            dep_miss_beta_1.job_run_id = beta_job_1_id.clone();
-            dep_miss_beta_1.missing_deps = vec![MissingDeps {
-                impacted: vec![PartitionRef {
-                    r#ref: "data/beta".to_string(),
-                }],
-                missing: vec![PartitionRef {
-                    r#ref: "data/alpha".to_string(),
-                }],
-            }];
-            events.push(Event::JobRunMissingDepsV1(dep_miss_beta_1));
-
-            // 5. Create derivative want for data/alpha
-            let alpha_want_id = "alpha-want".to_string();
-            let mut create_alpha = WantCreateEventV1::default();
-            create_alpha.want_id = alpha_want_id.clone();
-            create_alpha.partitions = vec![PartitionRef {
-                r#ref: "data/alpha".to_string(),
-            }];
-            events.push(Event::WantCreateV1(create_alpha));
-
-            // 6. Queue alpha job
-            let alpha_job_id = "alpha-job".to_string();
-            let mut buffer_alpha = JobRunBufferEventV1::default();
-            buffer_alpha.job_run_id = alpha_job_id.clone();
-            buffer_alpha.job_label = "//job_alpha".to_string();
-            buffer_alpha.want_attributed_partitions = vec![WantAttributedPartitions {
-                want_id: alpha_want_id.clone(),
-                partitions: vec![PartitionRef {
-                    r#ref: "data/alpha".to_string(),
-                }],
-            }];
-            buffer_alpha.building_partitions = vec![PartitionRef {
-                r#ref: "data/alpha".to_string(),
-            }];
-            events.push(Event::JobRunBufferV1(buffer_alpha));
-
-            // 7. Alpha job starts running
-            let mut heartbeat_alpha = JobRunHeartbeatEventV1::default();
-            heartbeat_alpha.job_run_id = alpha_job_id.clone();
-            events.push(Event::JobRunHeartbeatV1(heartbeat_alpha));
-
-            // 8. Alpha job succeeds
-            let mut success_alpha = JobRunSuccessEventV1::default();
-            success_alpha.job_run_id = alpha_job_id.clone();
-            events.push(Event::JobRunSuccessV1(success_alpha));
-
-            // 9. Queue beta job again (second attempt) - THIS IS THE CRITICAL MOMENT
-            let beta_job_2_id = "beta-job-2".to_string();
-            let mut buffer_beta_2 = JobRunBufferEventV1::default();
-            buffer_beta_2.job_run_id = beta_job_2_id.clone();
-            buffer_beta_2.job_label = "//job_beta".to_string();
-            buffer_beta_2.want_attributed_partitions = vec![WantAttributedPartitions {
-                want_id: beta_want_id.clone(),
-                partitions: vec![PartitionRef {
-                    r#ref: "data/beta".to_string(),
-                }],
-            }];
-            buffer_beta_2.building_partitions = vec![PartitionRef {
-                r#ref: "data/beta".to_string(),
-            }];
-            events.push(Event::JobRunBufferV1(buffer_beta_2));
-
-            // 10. Beta job starts running
-            let mut heartbeat_beta_2 = JobRunHeartbeatEventV1::default();
-            heartbeat_beta_2.job_run_id = beta_job_2_id.clone();
-            events.push(Event::JobRunHeartbeatV1(heartbeat_beta_2));
-
-            // 11. Beta job succeeds
-            let mut success_beta_2 = JobRunSuccessEventV1::default();
-            success_beta_2.job_run_id = beta_job_2_id.clone();
-            events.push(Event::JobRunSuccessV1(success_beta_2));
+            let (events, ids) = multihop_scenario();
 
             // Process all events - this simulates replay
+            let mut state = BuildState::default();
             for event in &events {
                 state.handle_event(event);
             }
 
             // Verify final state
-            let beta_want = state.get_want(&beta_want_id).unwrap();
+            let beta_want = state.get_want(&ids.beta_want_id).unwrap();
             assert_eq!(
                 beta_want.status,
                 Some(crate::WantStatusCode::WantSuccessful.into()),
                 "Beta want should be successful after multi-hop dependency resolution"
             );
 
-            let alpha_want = state.get_want(&alpha_want_id).unwrap();
+            let alpha_want = state.get_want(&ids.alpha_want_id).unwrap();
             assert_eq!(
                 alpha_want.status,
                 Some(crate::WantStatusCode::WantSuccessful.into()),

databuild/build_state/mod.rs

@@ -61,6 +61,11 @@ pub struct BuildState {
     // Inverted indexes
     pub(crate) wants_for_partition: BTreeMap<String, Vec<String>>, // partition ref → want_ids
     pub(crate) downstream_waiting: BTreeMap<String, Vec<Uuid>>, // upstream ref → partition UUIDs waiting for it
+
+    // Consumer index for lineage queries: input_uuid → list of (output_uuid, job_run_id)
+    // Uses UUIDs (not refs) to preserve historical lineage across partition rebuilds
+    // Populated from read_deps on job success
+    pub(crate) partition_consumers: BTreeMap<Uuid, Vec<(Uuid, String)>>,
 }
 
 impl BuildState {
@@ -118,6 +123,15 @@ impl BuildState {
             .unwrap_or(&[])
     }
 
+    /// Get consumers for a partition UUID (downstream partitions that read this one)
+    /// Returns list of (output_uuid, job_run_id) tuples
+    pub fn get_partition_consumers(&self, uuid: &Uuid) -> &[(Uuid, String)] {
+        self.partition_consumers
+            .get(uuid)
+            .map(|v| v.as_slice())
+            .unwrap_or(&[])
+    }
+
     /// Register a want in the wants_for_partition inverted index
     pub(crate) fn register_want_for_partitions(
         &mut self,

databuild/build_state/queries.rs

@@ -2,10 +2,12 @@
 //!
 //! Read-only methods for accessing state (get_*, list_*) used by the API layer.
 
+use crate::util::{HasRelatedIds, RelatedIds};
 use crate::{
-    JobRunDetail, ListJobRunsRequest, ListJobRunsResponse, ListPartitionsRequest,
-    ListPartitionsResponse, ListTaintsRequest, ListTaintsResponse, ListWantsRequest,
-    ListWantsResponse, PartitionDetail, TaintDetail, WantDetail,
+    GetJobRunResponse, GetPartitionResponse, GetWantResponse, JobRunDetail, ListJobRunsRequest,
+    ListJobRunsResponse, ListPartitionsRequest, ListPartitionsResponse, ListTaintsRequest,
+    ListTaintsResponse, ListWantsRequest, ListWantsResponse, PartitionDetail, RelatedEntities,
+    TaintDetail, WantDetail,
 };
 use std::collections::BTreeMap;
 
@@ -49,6 +51,7 @@ impl BuildState {
             match_count: self.wants.len() as u64,
             page,
             page_size,
+            index: None,
         }
     }
 
@@ -60,6 +63,7 @@ impl BuildState {
             match_count: self.wants.len() as u64,
             page,
             page_size,
+            index: None,
         }
     }
 
@@ -81,6 +85,7 @@ impl BuildState {
             match_count: self.canonical_partitions.len() as u64,
             page,
             page_size,
+            index: None,
         }
     }
 
@@ -102,6 +107,7 @@ impl BuildState {
             match_count: self.job_runs.len() as u64,
             page,
             page_size,
+            index: None,
         }
     }
 }
@@ -116,3 +122,214 @@ fn list_state_items<T: Clone>(map: &BTreeMap<String, T>, page: u64, page_size: u
         .cloned()
         .collect()
 }
+
+// ============================================================================
+// Response builders with RelatedEntities index
+// ============================================================================
+
+impl BuildState {
+    /// Resolve RelatedIds to a RelatedEntities index by looking up entities in BuildState.
+    /// This is the central method for building the index from collected IDs.
+    pub fn resolve_related_ids(&self, ids: &RelatedIds) -> RelatedEntities {
+        let mut index = RelatedEntities::default();
+
+        // Resolve partition refs
+        for partition_ref in &ids.partition_refs {
+            if !index.partitions.contains_key(partition_ref) {
+                if let Some(p) = self.get_canonical_partition(partition_ref) {
+                    index
+                        .partitions
+                        .insert(partition_ref.clone(), p.to_detail());
+                }
+            }
+        }
+
+        // Resolve partition UUIDs
+        for uuid in &ids.partition_uuids {
+            if let Some(p) = self.partitions_by_uuid.get(uuid) {
+                let detail = p.to_detail();
+                if let Some(ref pref) = detail.r#ref {
+                    if !index.partitions.contains_key(&pref.r#ref) {
+                        index.partitions.insert(pref.r#ref.clone(), detail);
+                    }
+                }
+            }
+        }
+
+        // Resolve job run IDs
+        for job_run_id in &ids.job_run_ids {
+            if !index.job_runs.contains_key(job_run_id) {
+                if let Some(jr) = self.job_runs.get(job_run_id) {
+                    index.job_runs.insert(job_run_id.clone(), jr.to_detail());
+                }
+            }
+        }
+
+        // Resolve want IDs
+        for want_id in &ids.want_ids {
+            if !index.wants.contains_key(want_id) {
+                if let Some(w) = self.wants.get(want_id) {
+                    index.wants.insert(want_id.clone(), w.to_detail());
+                }
+            }
+        }
+
+        index
+    }
+
+    /// Get a want with its related entities (job runs, partitions)
+    pub fn get_want_with_index(&self, want_id: &str) -> Option<GetWantResponse> {
+        let want = self.wants.get(want_id)?;
+        let want_detail = want.to_detail();
+        let ids = want.related_ids();
+        let index = self.resolve_related_ids(&ids);
+
+        Some(GetWantResponse {
+            data: Some(want_detail),
+            index: Some(index),
+        })
+    }
+
+    /// Get a partition with its related entities (builder job run, downstream consumers)
+    pub fn get_partition_with_index(&self, partition_ref: &str) -> Option<GetPartitionResponse> {
+        let partition = self.get_canonical_partition(partition_ref)?;
+        let partition_detail = partition.to_detail();
+
+        let mut ids = partition.related_ids();
+
+        // Add downstream consumers from the consumer index (not stored on partition)
+        let uuid = partition.uuid();
+        for (output_uuid, job_run_id) in self.get_partition_consumers(&uuid) {
+            if !ids.partition_uuids.contains(output_uuid) {
+                ids.partition_uuids.push(*output_uuid);
+            }
+            if !ids.job_run_ids.contains(job_run_id) {
+                ids.job_run_ids.push(job_run_id.clone());
+            }
+        }
+
+        // Add wants that reference this partition (from inverted index)
+        for want_id in self.get_wants_for_partition(partition_ref) {
+            if !ids.want_ids.contains(want_id) {
+                ids.want_ids.push(want_id.clone());
+            }
+        }
+
+        let index = self.resolve_related_ids(&ids);
+
+        Some(GetPartitionResponse {
+            data: Some(partition_detail),
+            index: Some(index),
+        })
+    }
+
+    /// Get a job run with its related entities (read/wrote partitions, derivative wants)
+    pub fn get_job_run_with_index(&self, job_run_id: &str) -> Option<GetJobRunResponse> {
+        let job_run = self.job_runs.get(job_run_id)?;
+        let job_run_detail = job_run.to_detail();
+        let ids = job_run.related_ids();
+        let index = self.resolve_related_ids(&ids);
+
+        Some(GetJobRunResponse {
+            data: Some(job_run_detail),
+            index: Some(index),
+        })
+    }
+
+    /// List wants with related entities index
+    pub fn list_wants_with_index(&self, request: &ListWantsRequest) -> ListWantsResponse {
+        let page = request.page.unwrap_or(0);
+        let page_size = request.page_size.unwrap_or(consts::DEFAULT_PAGE_SIZE);
+        let start = page * page_size;
+
+        let wants: Vec<_> = self
+            .wants
+            .values()
+            .skip(start as usize)
+            .take(page_size as usize)
+            .collect();
+
+        // Collect related IDs from all wants
+        let mut all_ids = RelatedIds::default();
+        for want in &wants {
+            all_ids.merge(want.related_ids());
+        }
+
+        let data: Vec<WantDetail> = wants.iter().map(|w| w.to_detail()).collect();
+        let index = self.resolve_related_ids(&all_ids);
+
+        ListWantsResponse {
+            data,
+            match_count: self.wants.len() as u64,
+            page,
+            page_size,
+            index: Some(index),
+        }
+    }
+
+    /// List partitions with related entities index
+    pub fn list_partitions_with_index(
+        &self,
+        request: &ListPartitionsRequest,
+    ) -> ListPartitionsResponse {
+        let page = request.page.unwrap_or(0);
+        let page_size = request.page_size.unwrap_or(consts::DEFAULT_PAGE_SIZE);
+        let start = page * page_size;
+
+        let partitions: Vec<_> = self
+            .canonical_partitions
+            .iter()
+            .skip(start as usize)
+            .take(page_size as usize)
+            .filter_map(|(_, uuid)| self.partitions_by_uuid.get(uuid))
+            .collect();
+
+        // Collect related IDs from all partitions
+        let mut all_ids = RelatedIds::default();
+        for partition in &partitions {
+            all_ids.merge(partition.related_ids());
+        }
+
+        let data: Vec<PartitionDetail> = partitions.iter().map(|p| p.to_detail()).collect();
+        let index = self.resolve_related_ids(&all_ids);
+
+        ListPartitionsResponse {
+            data,
+            match_count: self.canonical_partitions.len() as u64,
+            page,
+            page_size,
+            index: Some(index),
+        }
+    }
+
+    /// List job runs with related entities index
+    pub fn list_job_runs_with_index(&self, request: &ListJobRunsRequest) -> ListJobRunsResponse {
+        let page = request.page.unwrap_or(0);
+        let page_size = request.page_size.unwrap_or(consts::DEFAULT_PAGE_SIZE);
+        let start = page * page_size;
+
+        let job_runs: Vec<_> = self
+            .job_runs
+            .values()
+            .skip(start as usize)
+            .take(page_size as usize)
+            .collect();
+
+        // Collect related IDs from all job runs
+        let mut all_ids = RelatedIds::default();
+        for job_run in &job_runs {
+            all_ids.merge(job_run.related_ids());
+        }
+
+        let data: Vec<JobRunDetail> = job_runs.iter().map(|jr| jr.to_detail()).collect();
+        let index = self.resolve_related_ids(&all_ids);
+
+        ListJobRunsResponse {
+            data,
+            match_count: self.job_runs.len() as u64,
+            page,
+            page_size,
+            index: Some(index),
+        }
+    }
+}

databuild/databuild.proto

@@ -85,9 +85,11 @@ message JobRunHeartbeatEventV1 {
   string job_run_id = 1;
   // TODO reentrance?
 }
-// Simply indicates that the job has succeeded.
+// Indicates that the job has succeeded, including what data was read.
 message JobRunSuccessEventV1 {
   string job_run_id = 1;
+  // The read dependencies for this job run, preserving impacted→read relationships
+  repeated ReadDeps read_deps = 2;
 }
 // Simply indicates that the job has failed. Depending on retry logic defined in job, it may retry.
 message JobRunFailureEventV1 {
@@ -212,7 +214,10 @@ message WantDetail {
   optional string comment = 8;
   WantStatus status = 9;
   uint64 last_updated_timestamp = 10;
-  // TODO
+  // Lineage: all job runs that have serviced this want
+  repeated string job_run_ids = 11;
+  // Lineage: derivative wants spawned by this want's job dep-misses
+  repeated string derivative_want_ids = 12;
 }
 
 message PartitionDetail {
@@ -230,6 +235,11 @@ message PartitionDetail {
   // The unique identifier for this partition instance (UUID as string)
   // Each time a partition is built, it gets a new UUID derived from the job_run_id
   string uuid = 7;
+  // Lineage: job run that built this partition (for Live/Tainted partitions)
+  // Upstream lineage is resolved via this job run's read_deps (job run is source of truth)
+  optional string built_by_job_run_id = 8;
+  // Lineage: downstream partition UUIDs that consumed this (from consumer index)
+  repeated string downstream_partition_uuids = 9;
 }
 message PartitionStatus {
   PartitionStatusCode code = 1;
@@ -289,10 +299,26 @@ message JobRunDetail {
   optional uint64 last_heartbeat_at = 3;
   repeated PartitionRef building_partitions = 4;
   repeated WantAttributedPartitions servicing_wants = 5;
+  // Lineage: read dependencies with resolved UUIDs (for Succeeded jobs)
+  repeated ReadDeps read_deps = 6;
+  // Lineage: resolved UUIDs for read partitions (ref → UUID)
+  map<string, string> read_partition_uuids = 7;
+  // Lineage: resolved UUIDs for written partitions (ref → UUID)
+  map<string, string> wrote_partition_uuids = 8;
+  // Lineage: derivative wants spawned by this job's dep-miss (for DepMiss jobs)
+  repeated string derivative_want_ids = 9;
 }
 
 
 
+// Related entities index - used in API responses for deduplication and O(1) lookup
+// Each entity appears once in the index, even if referenced by multiple items in `data`
+message RelatedEntities {
+  map<string, PartitionDetail> partitions = 1;
+  map<string, JobRunDetail> job_runs = 2;
+  map<string, WantDetail> wants = 3;
+}
+
 message EventFilter {
   // IDs of wants to get relevant events for
   repeated string want_ids = 1;
@@ -308,6 +334,7 @@ message ListWantsResponse {
   uint64 match_count = 2;
   uint64 page = 3;
   uint64 page_size = 4;
+  RelatedEntities index = 5;
 }
 
 message ListTaintsRequest {
@@ -320,6 +347,7 @@ message ListTaintsResponse {
   uint64 match_count = 2;
   uint64 page = 3;
   uint64 page_size = 4;
+  RelatedEntities index = 5;
 }
 
 message ListPartitionsRequest {
@@ -332,6 +360,7 @@ message ListPartitionsResponse {
   uint64 match_count = 2;
   uint64 page = 3;
   uint64 page_size = 4;
+  RelatedEntities index = 5;
 }
 
 message ListJobRunsRequest {
@@ -344,6 +373,7 @@ message ListJobRunsResponse {
   uint64 match_count = 2;
   uint64 page = 3;
   uint64 page_size = 4;
+  RelatedEntities index = 5;
 }
 
 message CreateWantRequest {
@@ -372,6 +402,23 @@ message GetWantRequest {
 }
 message GetWantResponse {
   WantDetail data = 1;
+  RelatedEntities index = 2;
+}
+
+message GetPartitionRequest {
+  string partition_ref = 1;
+}
+message GetPartitionResponse {
+  PartitionDetail data = 1;
+  RelatedEntities index = 2;
+}
+
+message GetJobRunRequest {
+  string job_run_id = 1;
+}
+message GetJobRunResponse {
+  JobRunDetail data = 1;
+  RelatedEntities index = 2;
 }
 
 message CreateTaintRequest {

databuild/event_transforms.rs

@@ -30,6 +30,8 @@ impl From<WantCreateEventV1> for WantDetail {
             comment: e.comment,
             status: Some(WantStatusCode::WantIdle.into()),
             last_updated_timestamp: current_timestamp(),
+            job_run_ids: vec![],
+            derivative_want_ids: vec![],
         }
     }
 }
@@ -74,12 +76,17 @@ impl From<WantStatusCode> for WantStatus {
 
 impl From<JobRunBufferEventV1> for JobRunDetail {
     fn from(value: JobRunBufferEventV1) -> Self {
+        use std::collections::HashMap;
         Self {
             id: value.job_run_id,
             status: Some(JobRunStatusCode::JobRunQueued.into()),
             last_heartbeat_at: None,
             building_partitions: value.building_partitions,
             servicing_wants: value.want_attributed_partitions,
+            read_deps: vec![],
+            read_partition_uuids: HashMap::new(),
+            wrote_partition_uuids: HashMap::new(),
+            derivative_want_ids: vec![],
         }
     }
 }
@@ -210,7 +217,10 @@ impl Into<CreateWantResponse> for Option<WantDetail> {
 
 impl Into<GetWantResponse> for Option<WantDetail> {
     fn into(self) -> GetWantResponse {
-        GetWantResponse { data: self }
+        GetWantResponse {
+            data: self,
+            index: None,
+        }
     }
 }
 

databuild/http_server.rs

@@ -433,7 +433,7 @@ async fn list_wants_json(
                 .into_response();
         }
     };
-    let response = build_state.list_wants(&params);
+    let response = build_state.list_wants_with_index(&params);
 
     (StatusCode::OK, Json(response)).into_response()
 }
@@ -456,10 +456,8 @@ async fn get_want_json(
                 .into_response();
         }
     };
-    let response = build_state.get_want(&want_id);
-
-    match response {
-        Some(want) => (StatusCode::OK, Json(GetWantResponse { data: Some(want) })).into_response(),
+    match build_state.get_want_with_index(&want_id) {
+        Some(response) => (StatusCode::OK, Json(response)).into_response(),
         None => {
             tracing::debug!("Want not found: {}", want_id);
             (
@@ -608,7 +606,7 @@ async fn list_partitions_json(
                 .into_response();
         }
     };
-    let response = build_state.list_partitions(&params);
+    let response = build_state.list_partitions_with_index(&params);
 
     (StatusCode::OK, Json(response)).into_response()
 }
@@ -631,7 +629,7 @@ async fn list_job_runs_json(
                 .into_response();
         }
     };
-    let response = build_state.list_job_runs(&params);
+    let response = build_state.list_job_runs_with_index(&params);
 
     (StatusCode::OK, Json(response)).into_response()
 }

databuild/job_run.rs

@@ -256,6 +256,7 @@ impl SubProcessCompleted {
     pub fn to_event(&self, job_run_id: &Uuid) -> Event {
         Event::JobRunSuccessV1(JobRunSuccessEventV1 {
             job_run_id: job_run_id.to_string(),
+            read_deps: self.read_deps.clone(),
         })
     }
 }
@@ -394,6 +395,7 @@ impl ToEvent for SubProcessCompleted {
     fn to_event(&self, job_run_id: &Uuid) -> Event {
         Event::JobRunSuccessV1(JobRunSuccessEventV1 {
             job_run_id: job_run_id.to_string(),
+            read_deps: self.read_deps.clone(),
         })
     }
 }

databuild/job_run_state.rs

@@ -1,9 +1,11 @@
 use crate::partition_state::{BuildingPartitionRef, FailedPartitionRef, LivePartitionRef};
-use crate::util::current_timestamp;
+use crate::util::{HasRelatedIds, RelatedIds, current_timestamp};
 use crate::{
     EventSource, JobRunDetail, JobRunStatusCode, MissingDeps, PartitionRef, ReadDeps,
     WantAttributedPartitions,
 };
+use std::collections::BTreeMap;
+use uuid::Uuid;
 
 /// State: Job has been queued but not yet started
 #[derive(Debug, Clone)]
@@ -22,6 +24,12 @@ pub struct RunningState {
 #[derive(Debug, Clone)]
 pub struct SucceededState {
     pub completed_at: u64,
+    /// The read dependencies reported by the job, preserving impacted→read relationships
+    pub read_deps: Vec<ReadDeps>,
+    /// Resolved UUIDs for partitions that were read (ref → UUID at read time)
+    pub read_partition_uuids: BTreeMap<String, String>,
+    /// Resolved UUIDs for partitions that were written (ref → UUID)
+    pub wrote_partition_uuids: BTreeMap<String, String>,
 }
 
 /// State: Job failed during execution
@@ -113,11 +121,20 @@ impl JobRunWithState<RunningState> {
     }
 
     /// Transition from Running to Succeeded
-    pub fn succeed(self, timestamp: u64) -> JobRunWithState<SucceededState> {
+    pub fn succeed(
+        self,
+        timestamp: u64,
+        read_deps: Vec<ReadDeps>,
+        read_partition_uuids: BTreeMap<String, String>,
+        wrote_partition_uuids: BTreeMap<String, String>,
+    ) -> JobRunWithState<SucceededState> {
         JobRunWithState {
             info: self.info,
             state: SucceededState {
                 completed_at: timestamp,
+                read_deps,
+                read_partition_uuids,
+                wrote_partition_uuids,
             },
         }
     }
@@ -231,6 +248,21 @@ impl JobRunWithState<SucceededState> {
             .map(|p| LivePartitionRef(p.clone()))
             .collect()
     }
+
+    /// Get the read dependencies reported by the job
+    pub fn get_read_deps(&self) -> &[ReadDeps] {
+        &self.state.read_deps
+    }
+
+    /// Get the resolved UUIDs for partitions that were read
+    pub fn get_read_partition_uuids(&self) -> &BTreeMap<String, String> {
+        &self.state.read_partition_uuids
+    }
+
+    /// Get the resolved UUIDs for partitions that were written
+    pub fn get_wrote_partition_uuids(&self) -> &BTreeMap<String, String> {
+        &self.state.wrote_partition_uuids
+    }
 }
 
 impl JobRunWithState<FailedState> {
@@ -290,10 +322,128 @@ impl JobRunWithState<CanceledState> {
     }
 }
 
+// ==================== HasRelatedIds trait implementation ====================
+
+impl HasRelatedIds for JobRun {
+    /// Get the IDs of all entities this job run references.
+    /// Note: derivative_want_ids come from BuildState, not from JobRun itself.
+    fn related_ids(&self) -> RelatedIds {
+        // Partition refs from building_partitions (all states have this)
+        let partition_refs: Vec<String> = match self {
+            JobRun::Queued(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+            JobRun::Running(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+            JobRun::Succeeded(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+            JobRun::Failed(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+            JobRun::DepMiss(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+            JobRun::Canceled(jr) => jr
+                .info
+                .building_partitions
+                .iter()
+                .map(|p| p.r#ref.clone())
+                .collect(),
+        };
+
+        // Partition UUIDs from read/write lineage (only Succeeded state has these)
+        let partition_uuids: Vec<Uuid> = match self {
+            JobRun::Succeeded(jr) => {
+                let mut uuids = Vec::new();
+                for uuid_str in jr.state.read_partition_uuids.values() {
+                    if let Ok(uuid) = Uuid::parse_str(uuid_str) {
+                        uuids.push(uuid);
+                    }
+                }
+                for uuid_str in jr.state.wrote_partition_uuids.values() {
+                    if let Ok(uuid) = Uuid::parse_str(uuid_str) {
+                        if !uuids.contains(&uuid) {
+                            uuids.push(uuid);
+                        }
+                    }
+                }
+                uuids
+            }
+            _ => vec![],
+        };
+
+        // Want IDs from servicing_wants (all states have this)
+        let want_ids: Vec<String> = match self {
+            JobRun::Queued(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+            JobRun::Running(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+            JobRun::Succeeded(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+            JobRun::Failed(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+            JobRun::DepMiss(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+            JobRun::Canceled(jr) => jr
+                .info
+                .servicing_wants
+                .iter()
+                .map(|w| w.want_id.clone())
+                .collect(),
+        };
+
+        RelatedIds {
+            partition_refs,
+            partition_uuids,
+            job_run_ids: vec![],
+            want_ids,
+        }
+    }
+}
+
 // ==================== Conversion to JobRunDetail for API ====================
 
 impl JobRun {
     pub fn to_detail(&self) -> JobRunDetail {
+        use std::collections::HashMap;
+
         match self {
             JobRun::Queued(queued) => JobRunDetail {
                 id: queued.info.id.clone(),
@@ -301,6 +451,10 @@ impl JobRun {
                 last_heartbeat_at: None,
                 building_partitions: queued.info.building_partitions.clone(),
                 servicing_wants: queued.info.servicing_wants.clone(),
+                read_deps: vec![],
+                read_partition_uuids: HashMap::new(),
+                wrote_partition_uuids: HashMap::new(),
+                derivative_want_ids: vec![],
             },
             JobRun::Running(running) => JobRunDetail {
                 id: running.info.id.clone(),
@@ -308,6 +462,10 @@ impl JobRun {
                 last_heartbeat_at: Some(running.state.last_heartbeat_at),
                 building_partitions: running.info.building_partitions.clone(),
                 servicing_wants: running.info.servicing_wants.clone(),
+                read_deps: vec![],
+                read_partition_uuids: HashMap::new(),
+                wrote_partition_uuids: HashMap::new(),
+                derivative_want_ids: vec![],
             },
             JobRun::Succeeded(succeeded) => JobRunDetail {
                 id: succeeded.info.id.clone(),
@@ -315,6 +473,20 @@ impl JobRun {
                 last_heartbeat_at: None,
                 building_partitions: succeeded.info.building_partitions.clone(),
                 servicing_wants: succeeded.info.servicing_wants.clone(),
+                read_deps: succeeded.state.read_deps.clone(),
+                read_partition_uuids: succeeded
+                    .state
+                    .read_partition_uuids
+                    .clone()
+                    .into_iter()
+                    .collect(),
+                wrote_partition_uuids: succeeded
+                    .state
+                    .wrote_partition_uuids
+                    .clone()
+                    .into_iter()
+                    .collect(),
+                derivative_want_ids: vec![],
             },
             JobRun::Failed(failed) => JobRunDetail {
                 id: failed.info.id.clone(),
@@ -322,6 +494,10 @@ impl JobRun {
                 last_heartbeat_at: None,
                 building_partitions: failed.info.building_partitions.clone(),
                 servicing_wants: failed.info.servicing_wants.clone(),
+                read_deps: vec![],
+                read_partition_uuids: HashMap::new(),
+                wrote_partition_uuids: HashMap::new(),
+                derivative_want_ids: vec![],
             },
             JobRun::DepMiss(dep_miss) => JobRunDetail {
                 id: dep_miss.info.id.clone(),
@@ -329,6 +505,12 @@ impl JobRun {
                 last_heartbeat_at: None,
                 building_partitions: dep_miss.info.building_partitions.clone(),
                 servicing_wants: dep_miss.info.servicing_wants.clone(),
+                read_deps: dep_miss.state.read_deps.clone(),
+                read_partition_uuids: HashMap::new(),
+                wrote_partition_uuids: HashMap::new(),
+                // Note: derivative_want_ids would need to be populated from BuildState
+                // since the job doesn't track which wants it spawned (BEL does)
+                derivative_want_ids: vec![],
             },
             JobRun::Canceled(canceled) => JobRunDetail {
                 id: canceled.info.id.clone(),
@@ -336,6 +518,10 @@ impl JobRun {
                 last_heartbeat_at: None,
                 building_partitions: canceled.info.building_partitions.clone(),
                 servicing_wants: canceled.info.servicing_wants.clone(),
+                read_deps: vec![],
+                read_partition_uuids: HashMap::new(),
+                wrote_partition_uuids: HashMap::new(),
+                derivative_want_ids: vec![],
             },
         }
     }

databuild/orchestrator.rs

@@ -1073,6 +1073,8 @@ echo 'Beta succeeded'
                 comment: None,
                 status: None,
                 last_updated_timestamp: 0,
+                job_run_ids: vec![],
+                derivative_want_ids: vec![],
             }
         }
 

databuild/partition_state.rs

@@ -1,3 +1,4 @@
+use crate::util::{HasRelatedIds, RelatedIds};
 use crate::{PartitionDetail, PartitionRef, PartitionStatus, PartitionStatusCode};
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
@@ -58,6 +59,8 @@ pub struct UpstreamFailedState {
 pub struct TaintedState {
     pub tainted_at: u64,
     pub taint_ids: Vec<String>,
+    /// Job run that originally built this partition (before it was tainted)
+    pub built_by: String,
 }
 
 /// Generic partition struct parameterized by state.
@@ -250,6 +253,7 @@ impl PartitionWithState<LiveState> {
             state: TaintedState {
                 tainted_at: timestamp,
                 taint_ids: vec![taint_id],
+                built_by: self.state.built_by,
             },
         }
     }
@@ -337,9 +341,57 @@ impl Partition {
     pub fn is_tainted(&self) -> bool {
         matches!(self, Partition::Tainted(_))
     }
+}
 
+// ==================== HasRelatedIds trait implementation ====================
+
+impl HasRelatedIds for Partition {
+    /// Get the IDs of all entities this partition references.
+    /// Note: downstream_partition_uuids and want_ids come from BuildState indexes,
+    /// not from Partition itself.
+    fn related_ids(&self) -> RelatedIds {
+        // Job run ID from the builder (for states that track it)
+        let job_run_ids: Vec<String> = match self {
+            Partition::Building(p) => vec![p.state.job_run_id.clone()],
+            Partition::UpstreamBuilding(p) => vec![p.state.job_run_id.clone()],
+            Partition::UpForRetry(p) => vec![p.state.original_job_run_id.clone()],
+            Partition::Live(p) => vec![p.state.built_by.clone()],
+            Partition::Failed(p) => vec![p.state.failed_by.clone()],
+            Partition::UpstreamFailed(_) => vec![],
+            Partition::Tainted(p) => vec![p.state.built_by.clone()],
+        };
+
+        // Partition refs from missing deps (for UpstreamBuilding state)
+        let partition_refs: Vec<String> = match self {
+            Partition::UpstreamBuilding(p) => p
+                .state
+                .missing_deps
+                .iter()
+                .map(|d| d.r#ref.clone())
+                .collect(),
+            Partition::UpstreamFailed(p) => p
+                .state
+                .failed_upstream_refs
+                .iter()
+                .map(|d| d.r#ref.clone())
+                .collect(),
+            _ => vec![],
+        };
+
+        RelatedIds {
+            partition_refs,
+            partition_uuids: vec![],
+            job_run_ids,
+            want_ids: vec![],
+        }
+    }
+}
+
+impl Partition {
     /// Convert to PartitionDetail for API responses and queries.
-    /// Note: want_ids is now empty - this will be populated by BuildState from the inverted index.
+    /// Note: want_ids and downstream_partition_uuids are empty here and will be
+    /// populated by BuildState from its inverted indexes.
+    /// Upstream lineage is resolved via built_by_job_run_id → job run's read_deps.
     pub fn to_detail(&self) -> PartitionDetail {
         match self {
             Partition::Building(p) => PartitionDetail {
@@ -353,6 +405,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: None,
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: None,
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::UpstreamBuilding(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -365,6 +419,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: None,
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: None,
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::UpForRetry(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -377,6 +433,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: None,
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: None,
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::Live(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -389,6 +447,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: Some(p.state.built_at),
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: Some(p.state.built_by.clone()),
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::Failed(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -401,6 +461,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: Some(p.state.failed_at),
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: None,
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::UpstreamFailed(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -413,6 +475,8 @@ impl Partition {
                 taint_ids: vec![],
                 last_updated_timestamp: Some(p.state.failed_at),
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: None,
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
             Partition::Tainted(p) => PartitionDetail {
                 r#ref: Some(p.partition_ref.clone()),
@@ -421,10 +485,12 @@ impl Partition {
                     name: "PartitionTainted".to_string(),
                 }),
                 want_ids: vec![], // Populated by BuildState
-                job_run_ids: vec![],
+                job_run_ids: vec![p.state.built_by.clone()],
                 taint_ids: p.state.taint_ids.clone(),
                 last_updated_timestamp: Some(p.state.tainted_at),
                 uuid: p.uuid.to_string(),
+                built_by_job_run_id: Some(p.state.built_by.clone()),
+                downstream_partition_uuids: vec![], // Populated by BuildState
             },
         }
     }

databuild/util.rs

@@ -1,5 +1,57 @@
 use std::backtrace::Backtrace;
 use std::time::{SystemTime, UNIX_EPOCH};
+use uuid::Uuid;
+
+// ============================================================================
+// Related IDs - for building RelatedEntities index in API responses
+// ============================================================================
+
+/// IDs of related entities that an object references.
+/// Used by the query layer to build the RelatedEntities index for API responses.
+#[derive(Debug, Clone, Default)]
+pub struct RelatedIds {
+    /// Partition refs (e.g., from Want.partitions, JobRun.building_partitions)
+    pub partition_refs: Vec<String>,
+    /// Partition UUIDs (e.g., from read/write lineage, consumer index)
+    pub partition_uuids: Vec<Uuid>,
+    /// Job run IDs (e.g., from built_by, consumer jobs)
+    pub job_run_ids: Vec<String>,
+    /// Want IDs (e.g., derivative wants, upstream wants, servicing wants)
+    pub want_ids: Vec<String>,
+}
+
+impl RelatedIds {
+    /// Merge another RelatedIds into this one, deduplicating
+    pub fn merge(&mut self, other: RelatedIds) {
+        for r in other.partition_refs {
+            if !self.partition_refs.contains(&r) {
+                self.partition_refs.push(r);
+            }
+        }
+        for u in other.partition_uuids {
+            if !self.partition_uuids.contains(&u) {
+                self.partition_uuids.push(u);
+            }
+        }
+        for j in other.job_run_ids {
+            if !self.job_run_ids.contains(&j) {
+                self.job_run_ids.push(j);
+            }
+        }
+        for w in other.want_ids {
+            if !self.want_ids.contains(&w) {
+                self.want_ids.push(w);
+            }
+        }
+    }
+}
+
+/// Trait for entities that can report their related entity IDs.
+/// Used by the query layer to build RelatedEntities indexes for API responses.
+/// Implementing types: Want, JobRun, Partition
+pub trait HasRelatedIds {
+    fn related_ids(&self) -> RelatedIds;
+}
 
 pub fn current_timestamp() -> u64 {
     let now = SystemTime::now();
@@ -89,3 +141,173 @@ impl std::fmt::Display for DatabuildError {
         write!(f, "{}", self.msg)
     }
 }
+
+// ============================================================================
+// Test Scenarios - reusable BEL event sequences for testing
+// ============================================================================
+
+#[cfg(test)]
+pub mod test_scenarios {
+    use crate::data_build_event::Event;
+    use crate::{
+        JobRunBufferEventV1, JobRunHeartbeatEventV1, JobRunMissingDepsEventV1,
+        JobRunSuccessEventV1, MissingDeps, PartitionRef, ReadDeps, WantAttributedPartitions,
+        WantCreateEventV1,
+    };
+
+    /// IDs used in the multihop scenario for easy reference in tests
+    pub struct MultihopIds {
+        pub beta_want_id: String,
+        pub alpha_want_id: String,
+        pub beta_job_1_id: String,
+        pub beta_job_2_id: String,
+        pub alpha_job_id: String,
+    }
+
+    impl Default for MultihopIds {
+        fn default() -> Self {
+            Self {
+                beta_want_id: "beta-want".to_string(),
+                alpha_want_id: "alpha-want".to_string(),
+                beta_job_1_id: "beta-job-1".to_string(),
+                beta_job_2_id: "beta-job-2".to_string(),
+                alpha_job_id: "alpha-job".to_string(),
+            }
+        }
+    }
+
+    /// Creates a multihop dependency scenario:
+    /// 1. Want for data/beta is created
+    /// 2. Job beta-job-1 starts, discovers missing dep on data/alpha
+    /// 3. Derivative want for data/alpha is created
+    /// 4. Job alpha-job builds data/alpha successfully
+    /// 5. Job beta-job-2 retries and succeeds
+    ///
+    /// This exercises: want creation, job buffering, dep-miss, derivative wants,
+    /// job success with read_deps, and retry logic.
+    pub fn multihop_scenario() -> (Vec<Event>, MultihopIds) {
+        let ids = MultihopIds::default();
+        let mut events = vec![];
+
+        // 1. Create want for data/beta
+        events.push(Event::WantCreateV1(WantCreateEventV1 {
+            want_id: ids.beta_want_id.clone(),
+            partitions: vec![PartitionRef {
+                r#ref: "data/beta".to_string(),
+            }],
+            ..Default::default()
+        }));
+
+        // 2. Queue beta job (first attempt)
+        events.push(Event::JobRunBufferV1(JobRunBufferEventV1 {
+            job_run_id: ids.beta_job_1_id.clone(),
+            job_label: "//job_beta".to_string(),
+            want_attributed_partitions: vec![WantAttributedPartitions {
+                want_id: ids.beta_want_id.clone(),
+                partitions: vec![PartitionRef {
+                    r#ref: "data/beta".to_string(),
+                }],
+            }],
+            building_partitions: vec![PartitionRef {
+                r#ref: "data/beta".to_string(),
+            }],
+            ..Default::default()
+        }));
+
+        // 3. Beta job starts running
+        events.push(Event::JobRunHeartbeatV1(JobRunHeartbeatEventV1 {
+            job_run_id: ids.beta_job_1_id.clone(),
+            ..Default::default()
+        }));
+
+        // 4. Beta job reports missing dependency on data/alpha
+        events.push(Event::JobRunMissingDepsV1(JobRunMissingDepsEventV1 {
+            job_run_id: ids.beta_job_1_id.clone(),
+            missing_deps: vec![MissingDeps {
+                impacted: vec![PartitionRef {
+                    r#ref: "data/beta".to_string(),
+                }],
+                missing: vec![PartitionRef {
+                    r#ref: "data/alpha".to_string(),
+                }],
+            }],
+            ..Default::default()
+        }));
+
+        // 5. Create derivative want for data/alpha
+        events.push(Event::WantCreateV1(WantCreateEventV1 {
+            want_id: ids.alpha_want_id.clone(),
+            partitions: vec![PartitionRef {
+                r#ref: "data/alpha".to_string(),
+            }],
+            ..Default::default()
+        }));
+
+        // 6. Queue alpha job
+        events.push(Event::JobRunBufferV1(JobRunBufferEventV1 {
+            job_run_id: ids.alpha_job_id.clone(),
+            job_label: "//job_alpha".to_string(),
+            want_attributed_partitions: vec![WantAttributedPartitions {
+                want_id: ids.alpha_want_id.clone(),
+                partitions: vec![PartitionRef {
+                    r#ref: "data/alpha".to_string(),
+                }],
+            }],
+            building_partitions: vec![PartitionRef {
+                r#ref: "data/alpha".to_string(),
+            }],
+            ..Default::default()
+        }));
+
+        // 7. Alpha job starts running
+        events.push(Event::JobRunHeartbeatV1(JobRunHeartbeatEventV1 {
+            job_run_id: ids.alpha_job_id.clone(),
+            ..Default::default()
+        }));
+
+        // 8. Alpha job succeeds (no read deps for leaf node)
+        events.push(Event::JobRunSuccessV1(JobRunSuccessEventV1 {
+            job_run_id: ids.alpha_job_id.clone(),
+            read_deps: vec![],
+            ..Default::default()
+        }));
+
+        // 9. Queue beta job again (second attempt - retry)
+        events.push(Event::JobRunBufferV1(JobRunBufferEventV1 {
+            job_run_id: ids.beta_job_2_id.clone(),
+            job_label: "//job_beta".to_string(),
+            want_attributed_partitions: vec![WantAttributedPartitions {
+                want_id: ids.beta_want_id.clone(),
+                partitions: vec![PartitionRef {
+                    r#ref: "data/beta".to_string(),
+                }],
+            }],
+            building_partitions: vec![PartitionRef {
+                r#ref: "data/beta".to_string(),
+            }],
+            ..Default::default()
+        }));
+
+        // 10. Beta job 2 starts running
+        events.push(Event::JobRunHeartbeatV1(JobRunHeartbeatEventV1 {
+            job_run_id: ids.beta_job_2_id.clone(),
+            ..Default::default()
+        }));
+
+        // 11. Beta job 2 succeeds with read_deps showing it read data/alpha
+        events.push(Event::JobRunSuccessV1(JobRunSuccessEventV1 {
+            job_run_id: ids.beta_job_2_id.clone(),
+            read_deps: vec![ReadDeps {
+                impacted: vec![PartitionRef {
+                    r#ref: "data/beta".to_string(),
+                }],
+                read: vec![PartitionRef {
+                    r#ref: "data/alpha".to_string(),
+                }],
+            }],
+            ..Default::default()
+        }));
+
+        (events, ids)
+    }
+}

databuild/want_state.rs

@@ -1,5 +1,5 @@
 use crate::partition_state::FailedPartitionRef;
-use crate::util::current_timestamp;
+use crate::util::{HasRelatedIds, RelatedIds, current_timestamp};
 use crate::{EventSource, PartitionRef, WantCreateEventV1, WantDetail, WantStatusCode};
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
@@ -464,6 +464,35 @@ impl WantWithState<UpstreamBuildingState> {
     }
 }
 
+// ==================== HasRelatedIds trait implementation ====================
+
+impl HasRelatedIds for Want {
+    /// Get the IDs of all entities this want references.
+    /// Note: job_run_ids come from inverted indexes in BuildState, not from Want itself.
+    fn related_ids(&self) -> RelatedIds {
+        let partition_refs = self
+            .want()
+            .partitions
+            .iter()
+            .map(|p| p.r#ref.clone())
+            .collect();
+
+        // Collect want IDs from state-specific relationships
+        let want_ids = match self {
+            Want::UpstreamBuilding(w) => w.state.upstream_want_ids.clone(),
+            Want::UpstreamFailed(w) => w.state.failed_wants.clone(),
+            _ => vec![],
+        };
+
+        RelatedIds {
+            partition_refs,
+            partition_uuids: vec![],
+            job_run_ids: vec![],
+            want_ids,
+        }
+    }
+}
+
 // Helper methods on the Want enum
 impl Want {
     /// Create a new want in the Idle state
@@ -522,7 +551,9 @@ impl Want {
         }
     }
 
-    /// Convert to WantDetail for API responses and queries
+    /// Convert to WantDetail for API responses and queries.
+    /// Note: job_run_ids and derivative_want_ids are empty here and will be
+    /// populated by BuildState from its inverted indexes.
     pub fn to_detail(&self) -> WantDetail {
         WantDetail {
             want_id: self.want().want_id.clone(),
@@ -544,6 +575,8 @@ impl Want {
                 Want::UpstreamFailed(_) => Some(WantStatusCode::WantUpstreamFailed.into()),
                 Want::Canceled(_) => Some(WantStatusCode::WantCanceled.into()),
             },
+            job_run_ids: vec![],         // Populated by BuildState
+            derivative_want_ids: vec![], // Populated by BuildState
         }
     }
 }

databuild/web/templates.rs

@@ -3,7 +3,7 @@
 use askama::Template;
 
 use crate::{
-    JobRunDetail, JobRunStatus, PartitionDetail, PartitionRef, PartitionStatus,
+    JobRunDetail, JobRunStatus, PartitionDetail, PartitionRef, PartitionStatus, ReadDeps,
     WantAttributedPartitions, WantDetail, WantStatus,
 };
 
@@ -84,6 +84,9 @@ pub struct WantDetailView {
     pub comment_display: String,
     pub status: Option<WantStatusView>,
     pub last_updated_timestamp: u64,
+    // Lineage fields
+    pub job_run_ids: Vec<String>,
+    pub derivative_want_ids: Vec<String>,
 }
 
 impl From<&WantDetail> for WantDetailView {
@@ -99,6 +102,8 @@ impl From<&WantDetail> for WantDetailView {
             comment_display: w.comment.as_deref().unwrap_or("-").to_string(),
             status: w.status.as_ref().map(WantStatusView::from),
             last_updated_timestamp: w.last_updated_timestamp,
+            job_run_ids: w.job_run_ids.clone(),
+            derivative_want_ids: w.derivative_want_ids.clone(),
         }
     }
 }
@@ -119,6 +124,9 @@ pub struct PartitionDetailView {
     pub want_ids: Vec<String>,
     pub taint_ids: Vec<String>,
     pub uuid: String,
+    // Lineage fields
+    pub built_by_job_run_id: Option<String>,
+    pub downstream_partition_uuids: Vec<String>,
 }
 
 impl From<&PartitionDetail> for PartitionDetailView {
@@ -141,6 +149,8 @@ impl From<&PartitionDetail> for PartitionDetailView {
             want_ids: p.want_ids.clone(),
             taint_ids: p.taint_ids.clone(),
             uuid: p.uuid.clone(),
+            built_by_job_run_id: p.built_by_job_run_id.clone(),
+            downstream_partition_uuids: p.downstream_partition_uuids.clone(),
         }
     }
 }
@@ -165,16 +175,65 @@ impl From<&WantAttributedPartitions> for WantAttributedPartitionsView {
     }
 }
 
+/// View for read dependency entries (impacted → read relationships)
+pub struct ReadDepsView {
+    pub impacted: Vec<PartitionRefView>,
+    pub read: Vec<PartitionRefView>,
+}
+
+impl From<&ReadDeps> for ReadDepsView {
+    fn from(rd: &ReadDeps) -> Self {
+        Self {
+            impacted: rd.impacted.iter().map(PartitionRefView::from).collect(),
+            read: rd.read.iter().map(PartitionRefView::from).collect(),
+        }
+    }
+}
+
+/// View for partition ref with its resolved UUID (for lineage display)
+pub struct PartitionRefWithUuidView {
+    pub partition_ref: String,
+    pub partition_ref_encoded: String,
+    pub uuid: String,
+}
+
 pub struct JobRunDetailView {
     pub id: String,
     pub status: Option<JobRunStatusView>,
     pub last_heartbeat_at: Option<u64>,
     pub building_partitions: Vec<PartitionRefView>,
     pub servicing_wants: Vec<WantAttributedPartitionsView>,
+    // Lineage fields (populated for Succeeded/DepMiss states)
+    pub read_deps: Vec<ReadDepsView>,
+    pub read_partitions: Vec<PartitionRefWithUuidView>,
+    pub wrote_partitions: Vec<PartitionRefWithUuidView>,
+    pub derivative_want_ids: Vec<String>,
 }
 
 impl From<&JobRunDetail> for JobRunDetailView {
     fn from(jr: &JobRunDetail) -> Self {
+        // Build read_partitions from read_partition_uuids map
+        let read_partitions: Vec<PartitionRefWithUuidView> = jr
+            .read_partition_uuids
+            .iter()
+            .map(|(partition_ref, uuid)| PartitionRefWithUuidView {
+                partition_ref: partition_ref.clone(),
+                partition_ref_encoded: urlencoding::encode(partition_ref).into_owned(),
+                uuid: uuid.clone(),
+            })
+            .collect();
+
+        // Build wrote_partitions from wrote_partition_uuids map
+        let wrote_partitions: Vec<PartitionRefWithUuidView> = jr
+            .wrote_partition_uuids
+            .iter()
+            .map(|(partition_ref, uuid)| PartitionRefWithUuidView {
+                partition_ref: partition_ref.clone(),
+                partition_ref_encoded: urlencoding::encode(partition_ref).into_owned(),
+                uuid: uuid.clone(),
+            })
+            .collect();
+
         Self {
             id: jr.id.clone(),
             status: jr.status.as_ref().map(JobRunStatusView::from),
@@ -189,6 +248,10 @@ impl From<&JobRunDetail> for JobRunDetailView {
                 .iter()
                 .map(WantAttributedPartitionsView::from)
                 .collect(),
+            read_deps: jr.read_deps.iter().map(ReadDepsView::from).collect(),
+            read_partitions,
+            wrote_partitions,
+            derivative_want_ids: jr.derivative_want_ids.clone(),
         }
     }
 }
@@ -361,3 +424,91 @@ pub struct JobRunDetailPage {
 pub struct WantCreatePage {
     pub base: BaseContext,
 }
+
+// =============================================================================
+// Tests
+// =============================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::build_state::BuildState;
+    use crate::util::test_scenarios::multihop_scenario;
+    use askama::Template;
+
+    /// Helper to replay events into a fresh BuildState
+    fn build_state_from_events(events: &[crate::data_build_event::Event]) -> BuildState {
+        let mut state = BuildState::default();
+        for event in events {
+            state.handle_event(event);
+        }
+        state
+    }
+
+    mod want_detail_page {
+        use super::*;
+
+        /// Tests that the want detail page shows the job runs that serviced this want.
+        /// This is the "Fulfillment - Job Runs" section in the UI.
+        ///
+        /// Given: The multihop scenario completes (beta job dep-misses, alpha built, beta retries)
+        /// When: We render the beta want detail page
+        /// Then: It should show both beta job runs (beta-job-1 and beta-job-2)
+        #[test]
+        fn test_shows_servicing_job_runs() {
+            let (events, ids) = multihop_scenario();
+            let state = build_state_from_events(&events);
+
+            // Get beta want and render its detail page
+            let want_detail = state
+                .get_want(&ids.beta_want_id)
+                .expect("beta want should exist");
+            let template = WantDetailPage {
+                base: BaseContext::default(),
+                want: WantDetailView::from(want_detail),
+            };
+            let html = template.render().expect("template should render");
+
+            // Verify the Fulfillment section exists and contains both job run IDs
+            assert!(
+                html.contains(&ids.beta_job_1_id),
+                "Should show beta-job-1 in fulfillment section. HTML:\n{}",
+                html
+            );
+            assert!(
+                html.contains(&ids.beta_job_2_id),
+                "Should show beta-job-2 in fulfillment section. HTML:\n{}",
+                html
+            );
+        }
+
+        /// Tests that the want detail page shows derivative wants spawned by dep-miss.
+        /// This is the "Fulfillment - Derivative Wants" section in the UI.
+        ///
+        /// Given: The multihop scenario completes (beta job dep-misses, spawning alpha want)
+        /// When: We render the beta want detail page
+        /// Then: It should show the alpha want as a derivative
+        #[test]
+        fn test_shows_derivative_wants() {
+            let (events, ids) = multihop_scenario();
+            let state = build_state_from_events(&events);
+
+            // Get beta want and render its detail page
+            let want_detail = state
+                .get_want(&ids.beta_want_id)
+                .expect("beta want should exist");
+            let template = WantDetailPage {
+                base: BaseContext::default(),
+                want: WantDetailView::from(want_detail),
+            };
+            let html = template.render().expect("template should render");
+
+            // Verify the Fulfillment section exists and contains the derivative want
+            assert!(
+                html.contains(&ids.alpha_want_id),
+                "Should show alpha-want as derivative want. HTML:\n{}",
+                html
+            );
+        }
+    }
+}

databuild/web/templates/job_runs/detail.html

@@ -54,4 +54,43 @@
 </div>
 {% endif %}
 
+{% if !job_run.read_partitions.is_empty() %}
+<div class="detail-section">
+    <h2>Read Partitions ({{ job_run.read_partitions.len() }})</h2>
+    <ul class="partition-list">
+        {% for p in job_run.read_partitions %}
+        <li>
+            <a href="/partitions/{{ p.partition_ref_encoded }}" class="partition-ref">{{ p.partition_ref }}</a>
+            <span style="color:var(--color-text-muted);font-size:.75rem;font-family:monospace;margin-left:.5rem">uuid: {{ p.uuid }}</span>
+        </li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
+{% if !job_run.wrote_partitions.is_empty() %}
+<div class="detail-section">
+    <h2>Wrote Partitions ({{ job_run.wrote_partitions.len() }})</h2>
+    <ul class="partition-list">
+        {% for p in job_run.wrote_partitions %}
+        <li>
+            <a href="/partitions/{{ p.partition_ref_encoded }}" class="partition-ref">{{ p.partition_ref }}</a>
+            <span style="color:var(--color-text-muted);font-size:.75rem;font-family:monospace;margin-left:.5rem">uuid: {{ p.uuid }}</span>
+        </li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
+{% if !job_run.derivative_want_ids.is_empty() %}
+<div class="detail-section">
+    <h2>Derivative Wants ({{ job_run.derivative_want_ids.len() }})</h2>
+    <ul class="partition-list">
+        {% for id in job_run.derivative_want_ids %}
+        <li><a href="/wants/{{ id }}">{{ id }}</a></li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
 {% call base::footer() %}

databuild/web/templates/partitions/detail.html

@@ -32,9 +32,34 @@
     </div>
 </div>
 
+{% match partition.built_by_job_run_id %}
+{% when Some with (job_run_id) %}
+<div class="detail-section">
+    <h2>Lineage - Built By</h2>
+    <p>
+        <a href="/job_runs/{{ job_run_id }}">{{ job_run_id }}</a>
+        <span style="color:var(--color-text-muted);font-size:.75rem;margin-left:.5rem">(view job run for input partitions)</span>
+    </p>
+</div>
+{% when None %}
+{% endmatch %}
+
+{% if !partition.downstream_partition_uuids.is_empty() %}
+<div class="detail-section">
+    <h2>Lineage - Downstream Consumers ({{ partition.downstream_partition_uuids.len() }})</h2>
+    <ul class="partition-list">
+        {% for uuid in partition.downstream_partition_uuids %}
+        <li>
+            <span style="font-family:monospace;font-size:.8125rem">{{ uuid }}</span>
+        </li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
 {% if !partition.job_run_ids.is_empty() %}
 <div class="detail-section">
-    <h2>Job Runs ({{ partition.job_run_ids.len() }})</h2>
+    <h2>Related Job Runs ({{ partition.job_run_ids.len() }})</h2>
     <ul class="partition-list">
         {% for id in partition.job_run_ids %}
         <li><a href="/job_runs/{{ id }}">{{ id }}</a></li>

databuild/web/templates/wants/detail.html

@@ -65,4 +65,26 @@
 </div>
 {% endif %}
 
+{% if !want.job_run_ids.is_empty() %}
+<div class="detail-section">
+    <h2>Fulfillment - Job Runs ({{ want.job_run_ids.len() }})</h2>
+    <ul class="partition-list">
+        {% for id in want.job_run_ids %}
+        <li><a href="/job_runs/{{ id }}">{{ id }}</a></li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
+{% if !want.derivative_want_ids.is_empty() %}
+<div class="detail-section">
+    <h2>Fulfillment - Derivative Wants ({{ want.derivative_want_ids.len() }})</h2>
+    <ul class="partition-list">
+        {% for id in want.derivative_want_ids %}
+        <li><a href="/wants/{{ id }}">{{ id }}</a></li>
+        {% endfor %}
+    </ul>
+</div>
+{% endif %}
+
 {% call base::footer() %}

docs/narrative/what-llms-dont-do.md

@@ -0,0 +1,7 @@
+
+# What LLMs Don't Do
+
+- Create and cultivate technical strategy
+  - Don't have a specific vision of the organizing formalization of the problem + the technical solution
+- Adhere to technical strategy
+  - Please please please just read the relevant docs!

docs/plans/detail-lineage.md

@@ -0,0 +1,230 @@
+# Detail & Lineage Views
+
+## Vision
+
+Provide rich, navigable views into databuild's execution history that answer operational questions:
+
+- **"What work was done to fulfill this want?"** - The full DAG of partitions built and jobs run
+- **"Where did this data come from?"** - Trace a partition's lineage back through its inputs
+- **"What downstream data uses this?"** - Understand impact before tainting or debugging staleness
+
+## Three Distinct Views
+
+### 1. Want Fulfillment View
+
+Shows the work tree rooted at a want: all partitions built, jobs run, and derivative wants spawned to fulfill it.
+
+```
+W-001 "data/gamma" [Successful]
+│
+├── data/gamma [Live, uuid:abc]
+│   └── JR-789 [Succeeded]
+│       ├── read: data/beta [Live, uuid:def]
+│       └── read: data/alpha [Live, uuid:ghi]
+│
+└── derivative: W-002 "data/beta" [Successful]
+    │   └── triggered by: JR-456 dep-miss
+    │
+    └── data/beta [Live, uuid:def]
+        └── JR-456 [DepMiss → retry → Succeeded]
+            └── read: data/alpha [Live, uuid:ghi]
+```
+
+Key insight: This shows **specific partition instances** (by UUID), not just refs. A want's fulfillment is a concrete snapshot of what was built.
+
+### 2. Partition Lineage View
+
+The data flow graph: partition ↔ job_run alternating. Navigable upstream (inputs) and downstream (consumers).
+
+```
+              UPSTREAM
+                 │
+    ┌────────────┼────────────┐
+    ▼            ▼            ▼
+[data/a]    [data/b]    [data/c]
+    │            │            │
+    └────────────┼────────────┘
+                 ▼
+            JR-xyz [Succeeded]
+                 │
+                 ▼
+         ══════════════════
+         ║  data/beta     ║  ← FOCUS
+         ║  [Live]        ║
+         ══════════════════
+                 │
+                 ▼
+            JR-abc [Running]
+                 │
+    ┌────────────┼────────────┐
+    ▼            ▼            ▼
+[data/x]    [data/y]    [data/z]
+                 │
+              DOWNSTREAM
+```
+
+This view answers: "What data flows into/out of this partition?" Click to navigate.
+
+### 3. JobRun Detail View
+
+Not a graph - just the immediate context of a single job execution:
+
+- **Scheduled for**: Which want(s) triggered this job
+- **Read**: Input partitions (with UUIDs - the specific versions read)
+- **Wrote**: Output partitions (with UUIDs)
+- **Status history**: Queued → Running → Succeeded/Failed/DepMiss
+- **If DepMiss**: Which derivative wants were spawned
+
+## Data Requirements
+
+### Track read_deps on success
+
+Currently only captured on dep-miss. Need to extend `JobRunSuccessEventV1`:
+
+```protobuf
+message JobRunSuccessEventV1 {
+  string job_run_id = 1;
+  repeated ReadDeps read_deps = 2;  // NEW
+}
+```
+
+### Inverted consumer index
+
+To answer "what reads this partition", need:
+
+```rust
+partition_consumers: BTreeMap<Uuid, Vec<(Uuid, String)>>  // input_uuid → (output_uuid, job_run_id)
+```
+
+Indexed by UUID (not ref) because partition refs get reused across rebuilds, but UUIDs are immutable per instance. This preserves historical lineage correctly.
+
+Built from read_deps when processing JobRunSuccessEventV1.
+
+## Design Decisions
+
+1. **Retries**: List all job runs triggered by a want, collapsing retries in the UI (expandable)
+2. **Lineage UUIDs**: Resolve partition refs to canonical UUIDs at job success time (jobs don't need to know about UUIDs)
+3. **High fan-out**: Truncate to N items with "+X more" expansion
+4. **Consumer index by UUID**: Index consumers by partition UUID (not ref) since refs get reused across rebuilds but UUIDs are immutable per instance
+5. **Job run as lineage source of truth**: Partition details don't duplicate upstream info - they reference their builder job run, which holds the read_deps
+
+## API Response Pattern
+
+Detail and list endpoints return a wrapper with the primary data plus a shared index of related entities:
+
+```protobuf
+message GetJobRunResponse {
+  JobRunDetail data = 1;
+  RelatedEntities index = 2;
+}
+
+message ListJobRunsResponse {
+  repeated JobRunDetail data = 1;
+  RelatedEntities index = 2;  // shared across all items
+}
+
+message RelatedEntities {
+  map<string, PartitionDetail> partitions = 1;
+  map<string, JobRunDetail> job_runs = 2;
+  map<string, WantDetail> wants = 3;
+}
+```
+
+**Why this pattern:**
+- **No recursion** - Detail types stay flat, don't embed each other
+- **Deduplication** - Each entity appears once in the index, even if referenced by multiple items in `data`
+- **O(1) lookup** - Templates access `index.partitions["data/beta"]` directly
+- **Composable** - Same pattern works for single-item and list endpoints
+
+## Implementation Plan
+
+### ✅ Phase 1: Data Model (Complete)
+
+**1.1 Extend JobRunSuccessEventV1**
+
+```protobuf
+message JobRunSuccessEventV1 {
+  string job_run_id = 1;
+  repeated ReadDeps read_deps = 2;  // preserves impacted→read relationships
+}
+```
+
+**1.2 Extend SucceededState to store resolved UUIDs**
+
+```rust
+pub struct SucceededState {
+    pub succeeded_at: u64,
+    pub read_deps: Vec<ReadDeps>,                        // from event
+    pub read_partition_uuids: BTreeMap<String, Uuid>,    // ref → UUID at read time
+    pub wrote_partition_uuids: BTreeMap<String, Uuid>,   // ref → UUID (from building_partitions)
+}
+```
+
+UUIDs resolved by looking up canonical partitions when processing success event.
+
+**1.3 Add consumer index to BuildState**
+
+```rust
+// input_uuid → list of (output_uuid, job_run_id)
+partition_consumers: BTreeMap<Uuid, Vec<(Uuid, String)>>
+```
+
+Populated from `read_deps` when processing JobRunSuccessEventV1. Uses UUIDs (not refs) to preserve historical lineage across partition rebuilds.
+
+### ✅ Phase 2: API Response Pattern (Complete)
+
+**2.1 RelatedEntities wrapper**
+
+Added `RelatedEntities` message and `index` field to all Get*/List* responses.
+
+**2.2 HasRelatedIds trait**
+
+Implemented trait for Want, JobRun, Partition that returns the IDs of related entities. Query layer uses this to build the index.
+
+**2.3 Query methods**
+
+Added `*_with_index()` methods that collect related IDs via the trait and resolve them to full entity details.
+
+### ✅ Phase 3: Job Integration (Complete)
+
+Jobs already emit `DATABUILD_DEP_READ_JSON` and the full pipeline is wired up:
+
+1. **Job execution** (`job_run.rs`): `SubProcessBackend::poll` parses `DATABUILD_DEP_READ_JSON` lines from stdout and stores in `SubProcessCompleted.read_deps`
+2. **Event creation** (`job_run.rs`): `to_event()` creates `JobRunSuccessEventV1` with `read_deps`
+3. **Event handling** (`event_handlers.rs`): `handle_job_run_success()` resolves `read_partition_uuids` and `wrote_partition_uuids`, populates `partition_consumers` index
+4. **API serialization** (`job_run_state.rs`): `to_detail()` includes `read_deps`, `read_partition_uuids`, `wrote_partition_uuids` in `JobRunDetail`
+
+### ✅ Phase 4: Frontend (Complete)
+
+**4.1 JobRun detail page**
+
+Added to `job_runs/detail.html`:
+- "Read Partitions" section showing partition refs with UUIDs (linked to partition detail)
+- "Wrote Partitions" section showing partition refs with UUIDs (linked to partition detail)
+- "Derivative Wants" section showing wants spawned by dep-miss (linked to want detail)
+
+Extended `JobRunDetailView` with:
+- `read_deps: Vec<ReadDepsView>` - impacted→read dependency relationships
+- `read_partitions: Vec<PartitionRefWithUuidView>` - input partitions with UUIDs
+- `wrote_partitions: Vec<PartitionRefWithUuidView>` - output partitions with UUIDs
+- `derivative_want_ids: Vec<String>` - derivative wants from dep-miss
+
+**4.2 Partition detail page**
+
+Added to `partitions/detail.html`:
+- "Lineage - Built By" section showing the builder job run (linked to job run detail for upstream lineage)
+- "Lineage - Downstream Consumers" section showing UUIDs of downstream partitions
+
+Extended `PartitionDetailView` with:
+- `built_by_job_run_id: Option<String>` - job run that built this partition
+- `downstream_partition_uuids: Vec<String>` - downstream consumers from index
+
+**4.3 Want detail page**
+
+Added to `wants/detail.html`:
+- "Fulfillment - Job Runs" section listing all job runs that serviced this want
+- "Fulfillment - Derivative Wants" section listing derivative wants spawned by dep-misses
+
+Extended `WantDetailView` with:
+- `job_run_ids: Vec<String>` - all job runs that serviced this want
+- `derivative_want_ids: Vec<String>` - derivative wants spawned

examples/multihop/databuild.json

@@ -3,7 +3,7 @@
   "jobs": [
     {
       "label": "//examples/multihop:job_alpha",
-      "entrypoint": "./examples/multihop/job_alpha.sh",
+      "entrypoint": "./job_alpha.sh",
       "environment": {
         "JOB_NAME": "alpha"
       },
@@ -11,7 +11,7 @@
     },
     {
       "label": "//examples/multihop:job_beta",
-      "entrypoint": "./examples/multihop/job_beta.sh",
+      "entrypoint": "./job_beta.sh",
       "environment": {
         "JOB_NAME": "beta"
       },