# M0.8 — M0 composition gate

| Field | Value |
|---|---|
| Phase | M0 — Read-only spine |
| Size | M — 1–3 days |
| Status | ✅ Done |
| Flags | gate |
| Spec | inlined below |
| Blocks | all of M0 |

## Goal

Prove the parts compose and that the swappable part is genuinely swappable —
the properties no single M0 task owns.

## Facts (inlined — no spec read needed)

The claim this phase makes: **a new input kind is added by implementing
`RecordSource`, and nothing downstream changes.** If that is false, the crate
split bought nothing and the streaming work later will be a rewrite.

The gate proves it by adding a third source that resembles nothing already
supported, and asserting the rest of the pipeline is untouched.

Second claim: the whole phase is free. No model calls, so the gate is a CI job
that runs on every push without a gateway or credentials.

## Steps

1. Implement `SyntheticSource` in the test tree only — generates records from a
   seed, has no file format, and deliberately produces a record larger than the
   chunk budget and a run of empty-text records.
2. Assert `chunks()` handles it with **no change** to `mem-chunk`.
3. Assert dependency direction still holds (M0.1 assertion 3) after three sources
   exist — this is when someone is tempted to reach backwards.
4. Run `mem ingest --dry-run` over all three sources for one project and diff the
   summary against a committed expected file.
5. Wire the whole thing as a required CI job.

## Acceptance

- Three sources, one `RecordSource`, zero source-specific branches in `mem-chunk`
  or `mem-cli`.
- Dry-run summary diffs empty against the committed expectation.
- CI job passes with no network and no credentials.

## Verify

**Harness:** committed expected-output file, diffed. The script's output is the
review artifact.

**Integration test** — `tests/it_m0_gate.rs`:
1. `a1_third_source_needs_no_downstream_change` — `SyntheticSource` flows through
   `chunks()`; assert `git diff --stat crates/mem-chunk crates/mem-cli` is empty
   for the commit that added it (enforced by a CI step, not by the test binary).
2. `a2_no_source_specific_branches` — grep `crates/mem-chunk` and `crates/mem-cli`
   for the strings `pi:`, `claude:`, `sessionId`, `toolResult`; assert none
   appear outside `mem-ingest`.
3. `a3_dry_run_golden` — run the dry run over all three sources, diff against
   `expected/m0-gate.txt`; empty diff is the only pass.
4. `a4_offline` — the entire gate runs with networking disabled.
5. `a5_lossless_end_to_end` — records in equals records out, across all three
   sources composed.

**Command:** `cargo test --workspace m0_gate`

**False pass:**
- Adding `SyntheticSource` in a way that mirrors the pi format. It then exercises
  the same code path and proves nothing about generality. It must have no file,
  no header line, and an oversized record.
- Assertion 3 passing because the expected file was regenerated in the same
  commit. A changed `expected/` file in a diff is a claim that the contract
  changed, and must be reviewed as one.

## Traps

- Skipping assertion 2 because "obviously there are no source-specific branches".
  There will be — the first `if provenance.starts_with("pi:")` gets added to fix
  a real bug and is entirely reasonable in isolation.
- Letting the gate need credentials. The value of an offline gate is that it runs
  on every push; the moment it needs a gateway key it becomes a nightly job that
  nobody watches.

---

Background: [DESIGN.md](../DESIGN.md) — `mem-chunk`, Verification