# 2026-05-21

## Broker MCP Gateway — Slice 2 (read tools + session cache foundation)

Branch: `feat-tools-broker-mcp-gateway-read-tools`.

Built the read-side of the gateway: lazy-minted, per-email cached world tokens drive `mark_fetch` / `mark_list` / `mark_versions` against the worldPool. The remaining 10 tools still hit `notImplementedHandler`. Plan reference: `/plans/broker-https-gateway.md` v5.

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

- **Session cache is keyed by canonical verified email.** Plan v4 was subject-hash-keyed; investigated the existing Issuer.MintFiltered and found the broker already canonicalizes email and uses it as the ownership key across `/auth/callback`, `/me/install`, `/tokens` list/revoke, and audit logs. Two identity dimensions in one broker would have been confusing. Published v5 of the plan pinning email-keyed session cache as a Non-Negotiable, and updated the slice accordingly. Subject claim stays in id_token for log correlation but is not the cache key.
- **OQ#9 resolution: retry-on-401-after-mint with exponential backoff.** The kubelet → world Secret propagation lag means a freshly-minted token can land at the world before the projected-volume refresh has run; the world then 401s. Considered three options:
  - Sync wait via a world-side `/health/tokens?hash=...` endpoint → rejected (violates "no demarkus-server changes" Non-Negotiable).
  - Prewarm at MCP `initialize` → rejected (front-loads SIGHUPs for worlds the user may never touch).
  - **Retry-on-401 with exponential backoff (chosen)** — broker-only, narrow blast radius, matches `mutateSecret`'s optimistic-concurrency posture.

  Defaults: 6 attempts, 250ms → 8s exponential, ~16s of total waiting across attempts. Configurable via `cfg.Server.MCP.FirstMintMax*`. Distinguishes "fresh mint" 401s (retry with backoff — propagation race) from "cache hit" 401s (invalidate + immediately re-mint without sleeping — operator hand-revoked, sweeper retired, etc.).

- **Singleflight on `(canonicalEmail, worldName)` mints.** Concurrent first-call bursts for the same identity+world coalesce to one Issuer round-trip. Mitigates the "mint storm" risk on broker restart (every active plugin reconnects and re-mints simultaneously). `golang.org/x/sync/singleflight` added as a direct dep on `tools/`.
- **`MCPGatewayWith(version, dispatcher)` test seam.** Production `MCPGateway()` builds a real `*worldPool` (and registers it on `Server.mcpPool` so `CloseMCPGateway()` drains pooled QUIC connections during shutdown). Tests pass a `fakeDispatcher` to drive handlers without standing up a real QUIC server. Adds `Server.CloseMCPGateway()` which `main.go` calls after `mcpSrv.Shutdown` so in-flight tool calls finish before connections close.
- **`formatToolResult` duplicated (not hoisted) from `client/cmd/demarkus-mcp/formatResult`.** 20-line helper, stable. A `formatResultReference` copy in `mcp_tools_read_test.go` is asserted byte-equal to `formatToolResult` for several `fetch.Result` cases — that's the proxy-fidelity gate. If the local helper drifts, the parity test breaks before shipping; that's when hoisting to `client/mcpfmt` becomes the right call.
- **Tool URL shape rejects triple-slash (`mark:///foo`).** `parseToolURL` only accepts the canonical `mark://{worldName}/{path}` form. Considered fallback-parsing `mark:/team-a/foo` (single-slash, world-in-path) but rejected — silently re-interpreting the first path segment as the worldName would mask agent typos. Strict shape, clear error.
- **`tools/` module now `replace`s `client/`.** Pre-Flight 0 already hoisted `client/fetch` and `client/merge` to public, but the broker module didn't have the replace directive in place because Slice 1 didn't yet import client packages. Added in this slice; `go mod tidy` then promoted `client` and `x/sync` to direct deps.

### Bugs found during testing

- **Session-cache clock vs issuer clock.** `newIssuer(t, ...)` pins the issuer's clock to 2026-05-11 (so tokens expire 2026-05-12). The gateway's session cache uses `Server.clock` which defaults to `time.Now`. Result: every minted token's `expiresAt` was already in the past by the broker's clock, so the cache treated every entry as instantly expired. Fix in `newGatewayWithDispatcher`: pin `srv.clock` to the same date as `newIssuer`. Two tests (`TestHandleMarkFetchCacheHitReusesToken`, `TestDispatchReadCacheHit401InvalidatesAndReMints`) caught it; both pass after the clock alignment.
- **Singleflight test deadlock.** Initial design used `select { case ready <- struct{}{}: default: }` to signal the test the mint was in flight, but with select-default the very first sender would lose the signal if the main test wasn't yet reading. Main then blocked forever on `<-ready`. Fix: buffered `ready` channel (size 1). Pinned in the test comment.
- **LRU eviction test using `GetOrMint` as a probe was self-defeating.** Each "is this session still cached?" check via `GetOrMint` either re-minted (mutating LRU) or moved the session to the LRU front, perturbing the very state under inspection. Switched to a direct read of `c.sessions` under the mutex.

### Scope outcome vs plan estimate

- Production code: ~1100 LOC (plan estimate: ~400). Overshoot mostly in the retry loop + mintFuncFor closure + formatter duplication + worldPool dispatcher seam.
- Test code: ~1224 LOC (plan estimate: ~500). Many edge cases — parseToolURL, propagation-race retry exhaustion, cache-hit 401 invalidation, byte-for-byte parity. Worth it.
- `go test -race ./...` green across all modules. `pre-commit.sh` (fmt + vet + golangci-lint across protocol/server/client/tools) green.

### Next session — Slice 3 starting point

- `feat-tools-broker-mcp-gateway-write-tools` branch.
- `mark_publish` / `mark_append` / `mark_archive` handlers in `mcp_tools_write.go`. Reuse `sessionCache.GetOrMint` + `worldDispatcher` (extend interface with Publish/Append/Archive methods on `worldPool`).
- Conflict envelope follows local server's shape (`expected_version`, `on_conflict: "fail"` for Slice 3 — merge-candidate is Slice 6).
- World-side RBAC failure (`not-permitted`) surfaces as MCP tool error without retry (unlike `unauthorized` which triggers the propagation-race retry loop).


## Broker MCP Gateway — Slice 3 (write tools)

Branch: `feat-tools-broker-mcp-gateway-write-tools`. Slice 2 (PR #146) merged onto main as `7c529d4`.

Lit up the three write verbs (`mark_publish`, `mark_append`, `mark_archive`). All 6 of the 13 tools are real handlers now; the 7 federation tools still hit `notImplementedHandler` until Slices 4–5.

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

- **Refactored `dispatchRead` → `dispatchWithAuth(ctx, claims, worldName, op worldOp)`.** Closure-based: handlers capture per-verb args (path, body, expected_version, meta) in the closure; the retry loop only knows about token. The `readOp` enum + `dispatchOp` switch are gone. This was load-bearing for Slice 3 — without the refactor, writes would need their own retry loop and the cache-hit-401 + propagation-race semantics could silently diverge. Slice 4–5 federation tools will share the same dispatch path.
- **`on_conflict="merge"` rejected with explicit Slice 6 pointer.** Plan says "Slice 3 ships on_conflict=fail only; merge-candidate is Slice 6." The cleanest agent UX is: reject `merge` outright with a tool-error message that names Slice 6. Silently treating `merge` as `fail` would be a bait-and-switch — the agent thinks merge is being attempted when it isn't, and the world's response shape wouldn't carry the merge-candidate body the agent's prompt expects. **Default flipped to `fail`** for Slice 3; will flip back to `merge` when Slice 6 lands the candidate flow.
- **Publisher metadata derives `agent` from the canonical email, not the MCP session's client info.** The local demarkus-mcp uses `mcpserver.ClientSessionFromContext(ctx)` to get the MCP client name (e.g. "claude-code"). The broker doesn't have session-level client info on the tool-call context (the MCP layer's session info is one transport up). Using `canonicalEmail(claims.Email)` instead matches the broker's existing audit log identity dimension — so a write's `agent` field correlates with the broker's `/tokens` and `/me/install` audit entries. Operators reading world-side audit logs see a real identity instead of a generic "broker."
- **Append auto-resolve via `dispatchWithAuth(VERSIONS) → APPEND` runs both calls through the same dispatch wrapper.** Each call gets independent retry-on-401 budget. The singleflight + sessionCache from Slice 2 ensure the VERSIONS call and the APPEND call share whatever's already cached — typical case: one mint, two dispatches.
- **Compile-time guard added: `var _ mcpserver.ToolHandlerFunc = (*mcpGateway)(nil).handleMarkPublish`** (and append + archive). Catches a signature regression at build time instead of at AddTool registration time, where it would be a runtime nil-handler. Three lines, zero cost; same pattern would be cheap to extend across all 13 tools in a follow-up.
- **Conflict + not-permitted forward verbatim, not as tool errors.** Slice 2 surfaced `unauthorized` as a retry signal AND eventually as a tool error if retries exhausted. For writes, `conflict` and `not-permitted` are first-class world responses the agent acts on (re-fetch and retry, ask the operator for more scope, etc.). The plan's byte-for-byte proxy contract says forward them verbatim — that means `isError: false` on the MCP envelope; the "status: conflict" line in the formatted text is the signal. Tests pin this for both conflict (publish with version mismatch) and not-permitted (write op against a read-only token).

### Scope outcome vs plan estimate

- Production code: ~250 LOC new (mcp_tools_write.go) + ~140 LOC modified (dispatchWithAuth refactor, worldDispatcher interface extension, worldPool method additions, gateway wiring, gateway test pivot to mark_discover). **Total prod ~390 LOC vs plan ~250.** On the high side but the refactor was load-bearing.
- Test code: ~543 LOC new (mcp_tools_write_test.go) + ~60 LOC modified (fakeDispatcher extended with publish/append/archive scripted fns + writeCall record type). **Total tests ~600 LOC vs plan ~400.** Many edge cases — explicit version, auto-resolve, missing body/version, conflict pass-through, not-permitted pass-through, transport failure, on_conflict=merge rejection, on_conflict=unknown rejection, retry-inheritance, end-to-end via Streamable HTTP.
- `go test -race ./...` green across all 4 modules. `pre-commit.sh` (fmt + vet + golangci-lint × 4) green.

### Next session — Slice 4 starting point

- `feat-tools-broker-mcp-gateway-federation-read` branch.
- `mark_discover` / `mark_resolve` / `mark_backlinks` / `mark_graph` handlers in `mcp_tools_federation.go`.
- Federation tools delegate to whichever client library functions back the local MCP server's federation surface. Per the plan: "second-pass spike at start of Slice 4" to figure out the public API shape — Pre-Flight 0 hoisted `client/fetch` and `client/merge`, but federation may need additional hoists (`client/internal/index`, `client/internal/graphstore`, `client/internal/graph`, `client/internal/links`). Worth doing the spike before coding.
- These tools are read-only and don't change the session-cache shape; they reuse `dispatchWithAuth` for any tool that requires a world token, and pure local operations (e.g. `mark_backlinks` against the broker's own graph store) skip dispatch entirely.