databuild/docs/plans/detail-lineage.md

# 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<String, Vec<String>>  // partition_ref → consumer partition_refs
```

Built from read_deps on job success.

## 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

## Implementation Plan

### Phase 1: Data Model

**1.1 Extend JobRunSuccessEventV1**

```protobuf
message JobRunSuccessEventV1 {
  string job_run_id = 1;
  repeated ReadDeps read_deps = 2;  // NEW: 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_partition_ref → list of (output_partition_ref, job_run_id)
partition_consumers: BTreeMap<String, Vec<(String, String)>>
```

Populated from `read_deps` when processing JobRunSuccessEventV1.

### Phase 2: Extend Existing API Endpoints

**2.1 GET /api/wants/:id**

Add to response:
- `job_runs`: All job runs servicing this want (with status, partitions built)
- `derivative_wants`: Wants spawned by dep-miss from this want's jobs

**2.2 GET /api/partitions/:ref**

Add to response:
- `built_by`: Job run that built this partition (with read_deps + resolved UUIDs)
- `upstream`: Input partitions (refs + UUIDs) from builder's read_deps
- `downstream`: Consumer partitions (refs + UUIDs) from consumer index

**2.3 GET /api/job_runs/:id**

Add to response:
- `read_deps`: With resolved UUIDs for each partition
- `wrote_partitions`: With UUIDs
- `derivative_wants`: If DepMiss, the wants that were spawned

### Phase 3: Frontend

**3.1 Want detail page**

Add "Fulfillment" section:
- List of job runs (retries collapsed, expandable)
- Derivative wants as nested items
- Partition UUIDs linked to partition detail

**3.2 Partition detail page**

Add "Lineage" section:
- Upstream: builder job → input partitions (navigable)
- Downstream: consumer jobs → output partitions (truncated at N)

**3.3 JobRun detail page**

Add:
- "Read" section with partition refs + UUIDs
- "Wrote" section with partition refs + UUIDs
- "Derivative Wants" section (if DepMiss)

### Phase 4: Job Integration

Extend `DATABUILD_DEP_READ_JSON` parsing to run on job success (not just dep-miss). Jobs already emit this; we just need to capture it.

## Sequencing

1. Proto + state changes
2. Event handler updates
3. API response extensions
4. Frontend enhancements