First slice of the capacity simplification. Operator: *"just have two
capacity — overall per project agent count and max worktrees. Remove all
other capacities and counts."* Plus two later additions: **merge is
always 1, fixed**, and **worktrees off ⇒ limit by total agents only**.
Three independently revertable commits. No limiter is added anywhere;
one is deleted, one is made structurally absent, and one is pinned.
---
## 1. Merge concurrency ratcheted at 1 (test-only)
I was asked to add a limiter if merge concurrency could be raised. **It
cannot** — there is no setting, workflow property, pool or trait config
anywhere that raises it, so this adds no code and pins what already
holds.
Serialization lives in the **pump**: `drainMergeQueue`’s `mergeRunning`
re-entrancy latch, `activeMergeTaskId` as a single-slot identity, the
`mergeBodyInFlight` next-generation latch, and one `ProjectEngine` per
projectId.
**Not** in the merge-queue lease, which is a per-task ROW (`primaryKey
[projectId, taskId]`) — two tasks can hold leases simultaneously by
construction, and it has exactly one caller (the worktree-reuse
handoff). Ordinary merges never take it. A lease-level test would have
been describing an invariant that layer has never held.
The second half guards the other direction: a merge-concurrency
*setting* would not fail the pump ratchet — it would sit unread until
someone wired it up.
**Revert-proof:** deleting the latch → `expected 1 times, but got 2
times`; deleting the `finally` → latch-stuck; injecting
`maxConcurrentMerges: 2` → fails naming the key; injecting a
`maxParallelLanes` merge-trait field → fails naming the field. Sources
restored byte-identical after each injection.
## 2. `worktreesEnabled` — off means the worktree limit cannot bind
No worktrees-off mode existed (no
`worktreesEnabled`/`useWorktrees`/`worktreeMode` anywhere — only
worktree *configuration*).
**Why not `maxWorktrees: 0`, which needs no new key:** it deadlocks. `??
4` keeps `0` (not nullish), the gate is `used >= limit`, so `0 >= 0`
holds **on an empty board** and nothing ever dispatches — while the
operator-visible reason reads `gate=maxWorktrees; used=0/0`, a limiter
that looks like it is working while the board is dead. It also needs the
Command Center `{min:1}` clamp relaxed. So `0` costs the gate rewrite
*and* the clamp change *and* encodes a mode as a magic value.
**Off is absence, not a big number.** `resolveWorktreeCapacityLimit`
returns `number | null`; `ConcurrencyGateDiagnostic.maxWorktreesGate` is
now optional, so consulting a worktree limit in OFF mode does not
type-check. A gate holding `Infinity` can start binding again the moment
someone "fixes" a comparison; an absent gate cannot.
That paid for itself immediately: making it nullable surfaced a
**second, independent** worktree gate (`activeWorktrees >= maxWorktrees`
early-return) that a skip-by-convention approach would have missed
silently.
**Scope, deliberately:** this is a statement about *counting*, not
isolation. It does not make concurrent agents safe to share one checkout
and builds nothing toward that — the non-worktree paths that exist today
are fallbacks to the operator’s own tree, one of which caused FN-8600.
**Revert-proof:** a resolver ignoring the flag turns both OFF scheduler
tests red while every ON test stays green — they reuse the *same*
fixture (5 in-progress, limit 4) that pre-existing tests prove blocks,
so the pair moves in opposite directions. Removing `disabled:` reddens
the UI test.
## 3. `maxTriageConcurrent` deleted — it controlled nothing
**Measured: zero enforcement reads.** The only `.maxTriageConcurrent`
reference in the repo was a route echoing it back in `/config`. FN-8453
removed the pool it gated and left the knob shipping in
`DEFAULT_SETTINGS`, the settings type, the section registry, the API
response and six i18n catalogs, doing nothing, for releases.
Historical FNXC comments are **updated, not deleted** — they explain a
real past incident; they now say "planning admission slot" so they stop
implying a live setting. Tombstoned so it cannot return.
`/config` loses a field; safe in-repo since `fetchConfig`’s own return
type never declared it.
---
## Two corrections worth recording
- I earlier reported `maxWorktrees` had **no** Settings UI. Wrong —
`WorktreesSection.tsx:47`; my grep was truncated by `head`. It changed
the placement (toggle beside it, rather than a duplicate key in
Scheduling).
- I planned to assert the queued-reason string is rewritten in OFF mode.
Measured that it is **unreachable**: when `maxConcurrent` binds, the
sweep bails before the per-task reason and logs nothing. The test
asserts absence instead.
Two near-misses caught before commit: a pre-existing FN-7505 guard
caught my *new* key missing a description mapping; and editing i18n via
`json.load/dump` silently dropped unrelated duplicate keys
(`autoUpdateAndRestart` in `fr`) — Python keeps only the last of a
duplicated key. Redone textually, every catalog re-validated.
## Verification
`pnpm lint` clean · core/engine/dashboard/i18n typecheck clean · `pnpm
test:gate` green (309 + 10 + 71) · capacity/worktree suites 11/11 ·
engine merge-invariant + scheduler 45/45 · dashboard settings 114/114.
Rebased onto current main and re-verified.
Nothing was booted at any point.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added a project setting to enable or disable running tasks in
worktrees.
* Disabling worktrees removes worktree capacity limits from task
scheduling.
* The “Max Worktrees” setting is disabled when worktree execution is
turned off.
* **Changes**
* Removed the unused triage concurrency setting from configuration and
dashboard responses.
* Updated scheduling diagnostics and queue messages to reflect disabled
worktree capacity limits.
* Added localized labels and help text for the new setting.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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