Memory held, not hit: slow or refuse new processes in a Small child near its limit before any stop #11994

A child forge near its memory limit now starts no new agent run or check while one of its own is already running. This is the first part of #11980. The rest of it is not done.

What changed

• New src/runs/memory_hold.ts. A cell child reads its own cgroup's anonymous memory, leaving the page cache out. At or above 75% of its limit, with at least one of its own runs going, memoryHold returns a sentence saying why nothing new starts. With nothing running a start is always allowed, so the hold can't last. A forge that isn't a cell child is never held.
• src/crew/dispatch.ts: a queued agent run in that state stays queued, with one log line. It is recorded under a new hold cause, memory (src/runs/held.ts), so vitals counts it as held on purpose rather than as waiting.
• src/checks/service.ts: checks stay queued while memory is tight and something is in flight, with one log line each. In practice checks run one at a time.
• Both services take an optional pressure option (added to CrewOptions in src/crew/runner.ts and ChecksOptions) so a test can supply a reading.
• docs/features/memory-held.md describes the behaviour.

Tests

• bun x tsc --noEmit, bun scripts/gate.ts, the new test/memory-hold.test.ts and the neighbouring checks-queue, vitals and crew-held suites all pass.
• scripts/fast.ts named 2206 of 2995 test files, so I ran those neighbouring suites instead.
• test/memory-hold.test.ts covers only the decision rule. There is no test that drives a real dispatcher or check queue under pressure; the existing stand-in crew helper was too heavy for the budget. That is the gap to look at in review.

Not done

• A smaller Bun heap (--smol) for the child's processes.
• Reclaiming idle app cells.
• A stop that takes only the largest process rather than the whole forge.
• Fault 1: a first ask on a claimed forge is still filed on <name>/forge. The steward says it probably matters most for staying inside 2 GiB.
• Fault 4: the real-cell proof on a 2 GiB, 1-core child.

The earlier scout branch for this issue doesn't exist on the remote, so none of its work was reused.

To try it Set FORGE_CELL_SIZE=small and point FORGE_CELL_CGROUP_DIR at a cgroup that sits above 75% of its limit while a run is going. New runs and checks then log "this forge holds N% of its memory; new work waits for a running one to finish".

Closes #11980

A child forge near its memory limit now starts no new agent run or check while one of its own is already running. This is the first part of #11980. The rest of it is not done.

What changed

• New src/runs/memory_hold.ts. A cell child reads its own cgroup's anonymous memory, leaving the page cache out. At or above 75% of its limit, with at least one of its own runs going, memoryHold returns a sentence saying why nothing new starts. With nothing running a start is always allowed, so the hold can't last. A forge that isn't a cell child is never held.
• src/crew/dispatch.ts: a queued agent run in that state stays queued, with one log line. It is recorded under a new hold cause, memory (src/runs/held.ts), so vitals counts it as held on purpose rather than as waiting.
• src/checks/service.ts: checks stay queued while memory is tight and something is in flight, with one log line each. In practice checks run one at a time.
• Both services take an optional pressure option (added to CrewOptions in src/crew/runner.ts and ChecksOptions) so a test can supply a reading.
• docs/features/memory-held.md describes the behaviour.

Tests

• bun x tsc --noEmit, bun scripts/gate.ts, the new test/memory-hold.test.ts and the neighbouring checks-queue, vitals and crew-held suites all pass.
• scripts/fast.ts named 2206 of 2995 test files, so I ran those neighbouring suites instead.
• test/memory-hold.test.ts covers only the decision rule. There is no test that drives a real dispatcher or check queue under pressure; the existing stand-in crew helper was too heavy for the budget. That is the gap to look at in review.

Not done

• A smaller Bun heap (--smol) for the child's processes.
• Reclaiming idle app cells.
• A stop that takes only the largest process rather than the whole forge.
• Fault 1: a first ask on a claimed forge is still filed on <name>/forge. The steward says it probably matters most for staying inside 2 GiB.
• Fault 4: the real-cell proof on a 2 GiB, 1-core child.

The earlier scout branch for this issue doesn't exist on the remote, so none of its work was reused.

To try it Set FORGE_CELL_SIZE=small and point FORGE_CELL_CGROUP_DIR at a cgroup that sits above 75% of its limit while a run is going. New runs and checks then log "this forge holds N% of its memory; new work waits for a running one to finish".

The failed check was the gate's 100-column comment rule. I rewrapped the three lines it named and pushed, so the check should re-run on the new commit.

The lines were in src/crew/dispatch.ts, src/crew/runner.ts and src/runs/memory_hold.ts; wording is unchanged apart from a few words trimmed to fit.

After the fix, bun scripts/gate.ts and bun x tsc --noEmit both pass, and the new memory-hold tests passed on the earlier run, before the rewrap. I haven't seen the forge's result yet.

This pull is still only part of #11980. It holds new agent runs and checks near the memory limit. It does not do the smaller Bun heap, reclaiming idle app cells, stopping only the largest process, or the real-cell proof.

A Small child near its memory limit now holds a queued agent run or a second check, and tests cover both the dispatcher and the check queue. bun scripts/gate.ts and bun x tsc --noEmit printed nothing; I did not look at their exit codes. I ran test/memory-hold.test.ts, checks-queue, vitals-held-agent and capacity (40 pass), but not bun scripts/design-lint.ts. Its output was cut off by the fast.ts listing, and nothing under src/web/ changed.

What the hold does. At or over 75% of the cgroup limit in anonymous memory, with one of its own runs already going, the child starts nothing new. Both the agent queue and the check queue use it. With nothing running a start is always allowed, so the hold never lasts. A forge that is not a cell child never holds.

Changes since review

• Dispatcher test: it drives pump() with a pressure stub and one run in inFlight. The queued run stays queued, heldRuns gives "memory", and the run log says so once across two pumps.
• Vitals test: the same test reads the real vitals card. With every queued run held there is no stalled-queue card. With another run waiting beside it, the card says "held on purpose: 1 by the forge's memory near its limit." No TUI screen was added, as you asked.
• Check-queue test: it runs the real check service with concurrency 2 and a pressure stub. One check holds a slot, and a second stays queued with the "queued, this forge holds 90% …" log line. When the pressure drops it runs and passes.
• Revert check: I removed the memoryHold call from dispatch.ts and service.ts and both new tests fail. Restored.
• slotted() (1): the check-queue hold now counts slotted(), not inFlight.size, so a verification-lane run no longer holds back a real check. I did not add a test with a verification run in flight.
• Cached reading (2): childPressure reuses its cgroup reading for 1 second (READING_MS), keyed by cgroup directory and with the clock passed in. A test shows the second read within the window is served from the cache and the next one after it is fresh.
• Docs: docs/features/memory-held.md mentions the cache and the new tests.

Not done. There is no real-cgroup test, because the sandbox has no cell child. The pressure source is covered by the stub, and by the cached-reading test, which reads fake cgroup files.

Try it. bun test test/memory-hold.test.ts. On a Small cell child, FORGE_CELL_SIZE and the cgroup do the rest.

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The two gate failures are fixed and pushed. bun scripts/gate.ts now exits 0, bun x tsc --noEmit printed nothing (I did not look at its exit code), and test/memory-hold.test.ts passes (7 tests). I did not run the other test files again, since only a comment and a marker changed.

• Comment wrap: the comment above READING_MS in src/runs/memory_hold.ts was 113 columns. It is now under 100.
• Real timer: the Bun.sleep(100) in test/memory-hold.test.ts is kept and marked // real-timer:. That wait is the test: it lets several 20 ms ticks pass to show the second check never starts while memory is held. A stepped clock would not show that, because the check queue has no clock to inject.

The gate reads committed changes (git diff against the base), so edits show up in its output only after a commit.

The pull description from my last message still applies unchanged.

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