# 2026-05-22

## Broker MCP Gateway — Slice 6 (conflict-aware merge in mark_publish)

Branch: `feat-tools-broker-mcp-gateway-merge`. Slice 4b+5 (PR #149) merged onto main as `fa9f86d`.

Lit up the `on_conflict="merge"` candidate flow in `mark_publish`. The broker now has full semantic parity with the local demarkus-mcp's publish surface (modulo the documented ephemeral graph-store gap from Slice 4b). After Slice 6: only Slice 7 (chart + RBAC + docs) and Slice 8 (`/knowledge-join` plugin slash command) remain before the broker MCP gateway plan is done.

### Decisions made this session that weren't in the plan

- **`brokerMergeAdapter` captures `ctx` in the struct.** Normally a code smell, but `merge.Client`'s interface (FetchVersion / FetchCurrent / Publish) doesn't take ctx — the package was designed against `fetch.Client` which also doesn't take ctx. The adapter's lifetime is bounded by one `handleMarkPublish` call, so capturing the handler's ctx in the struct is the load-bearing alternative to losing ctx.Done propagation across the 3-step orchestration. Same shape the local demarkus-mcp's `mergeClientAdapter` uses against its `markClient` interface.
- **Default `on_conflict` flipped to `"merge"` to match local demarkus-mcp.** Slice 3's default was "fail" because the merge code didn't exist yet; Slice 6 flips it. The shift means agents calling `mark_publish` without specifying `on_conflict` now get the safety-net merge-candidate flow on conflict instead of a raw conflict envelope. Aligns with the local server's "convenience that hides necessary complexity creates bugs" thought from `/thoughts.md` — merge as default is the safer footgun-free choice.
- **`optionalIntMeta` (vs the local `optionalInt`) to avoid name collision.** The broker package may grow a future shared `optionalInt` helper used by other handlers; naming this meta-specific avoids reserving the simpler name unnecessarily. Same behavior as the local server's helper.
- **`formatMergeOutcome` is duplicated, not hoisted.** Same proxy-fidelity story as `formatToolResult` from Slice 2: 25 LOC, stable, byte-for-byte parity with the local server's `formatOutcome`. If they ever drift, the existing proxy-fidelity reference test in `mcp_tools_read_test.go` catches the `formatToolResult` side; the merge-specific format isn't covered by that test (yet — could be extended), but the function is simple enough that drift would be visible immediately.

### Real bugs surfaced during testing

- **Append + auto-resolve happy-path test had `"server-version": "1.0"` in fixture data.** Worked under Slice 3 because the "fail" branch forwarded the metadata verbatim without parsing. Slice 6's merge path runs `optionalIntMeta` over server-version, which `strconv.Atoi`-rejects floats. Fixed the fixture to `"1"` (matches actual server output). The other append-side tests using "1.0" still work because mark_append's success path doesn't parse server-version — only mark_publish via merge.
- **`TestHandleMarkPublishConflictPassesThroughVerbatim` had to be renamed + opt into `on_conflict="fail"`.** Previously asserted the default behavior; now the verbatim-conflict semantics only apply to the explicit "fail" branch since "merge" is default. Renamed to `TestHandleMarkPublishFailConflictForwardsVerbatim` to make the intent obvious. The test still exists and pins the still-supported opt-out behavior.
- **`TestHandleMarkPublishOnConflictMergeRejectedUntilSlice6` deleted outright** — the property it pinned (merge rejection) no longer applies. Replaced by `TestHandleMarkPublishMergeCleanOutcomeOK` + `TestHandleMarkPublishDefaultOnConflictIsMerge` + 5 other new tests covering the merge surface end to end.
- **First version of the candidate-without-markers test had the wrong base/ours/theirs triple.** Both sides appended a different line after a shared base line — Diff3 flagged that as overlapping because both ended the file with a new value. Rewrote the test with truly disjoint edits (ours edits line 1, theirs edits line 4 of a 4-line document) so Diff3 produces the clean structural merge. Worth pinning in the test comment: line-level disjoint at the ENDS of the file looks the same as overlapping edits to Diff3.

### Scope outcome vs plan estimate

- Production code: +163 LOC in `mcp_tools_write.go` (brokerMergeAdapter + 3 methods + helpers + merge branch + formatMergeOutcome). Plan estimate ~150 LOC. ✅
- Test code: +375 LOC in `mcp_tools_write_test.go` (3 deleted/replaced, 7 new). Plan estimate ~250 LOC. Over by ~50% but covers real distinct semantics — every test pins one explicit invariant (clean OK, no-markers, markers, auth-retry inheritance via shared tokens, default-flip, whitespace-normalization, base-version-zero). Worth it.
- `go test -race ./...` green across all 4 modules. `pre-commit.sh` (fmt + vet + golangci-lint × 4) green.

### Surface status after Slice 6

All 13 broker MCP tools have full semantic parity with the local demarkus-mcp:

- 6 verbs (fetch/list/versions/publish/append/archive) with proxy fidelity + auth-race retry.
- 2 federation reads (discover/resolve).
- 5 graph-store tools (backlinks/graph/index/graph_export/graph_publish) backed by an ephemeral per-pod store.

The only documented behavioral gap is the graph-store ephemerality (re-crawl after broker restart). Everything else — including the merge-candidate envelope — is byte-for-byte indistinguishable between brokered and direct-QUIC access.

### Next session — Slice 7 starting point

Slice 7 is the chart, RBAC, docs work. Per the plan:

- `deploy/helm/demarkus-broker/values.yaml` — `server.mcp.addr`, `server.mcp.tls.existingSecretRef`, `server.mcp.sessionMaxIdle`, `server.mcp.worldTokenTTL`, `server.mcp.worldPool`. `worlds[].internalAddress` for non-default Service DNS overrides.
- Chart templates: deployment.yaml (new containerPort + TLS mount), service.yaml (gateway port), ingress.yaml (route mcp host to new port), networkpolicy.yaml (allow ingress on mcp port).
- `deploy/helm/demarkus-broker/README.md` — "MCP gateway" section. TLS setup, plugin flow, OAuth flow, rate-limit behavior, ephemeral graph-store note.
- `tools/demarkus-broker/MCP-API.md` — operator/developer-facing spec for the 13-tool MCP surface.
- Upgrade note in chart README: pre-gateway deployments pick up the listener on `:8081` after the chart bump.

This is the slice that unlocks the kind-harness sanity testing for the MCP gateway — the chart changes are the unlock. Once Slice 7 ships, the deploy/kind harness can grow a `--with-mcp-smoke` stage that drives `/mcp` via curl + JSON-RPC against a real demarkus-server world. That's the end-to-end "Done When" criterion from the plan.

Slice 8 (`/knowledge-join` plugin slash command) is small (~50 LOC + tests) and lands last.