workflow-fix: OOM-protect detached VM-side compute phases (choom -600 + pivot rule)

Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from a workflow-fix candidate raised on task #811 (emitting agent: orchestrator).

Goal

Document + mechanize OOM protection for VM-side detached long compute phases: the Step 9 entry-guard § "Detached VM-side long compute phases" launch shape should include an earlyoom-protection step (sudo choom -n -600 on the detached pid) and name the earlyoom collateral-kill failure mode.

Workflow gap

• Bug observed: #811's off-instance STAGE=fits (detached setsid per #833, ~5h projected) was SIGTERM-killed by earlyoom at ~2h (rc=143, 0 checkpoints written) when a NEIGHBOR process spiked VM memory 50%->10% in 23 min; the fit's own RSS was 6.8 GiB — earlyoom picked it by badness (1002) despite it not being the spiker. ~2h of compute lost.
• Why it is a workflow gap: the #833 detached-launch convention (SKILL.md Step 9 entry guard) hardens against session-kill-domain death but says nothing about earlyoom on the shared VM — any long VM-side detached phase is exposed to collateral kills from fleet co-tenancy, and the convention has no protection or pivot guidance.
• Confidence (emitter): medium

Proposed change (candidate diff sketch — refine in planning)

.claude/skills/issue/SKILL.md § "Detached VM-side long compute phases":
+ After the pid-identity verify, protect the phase from earlyoom collateral
+ kills: `sudo -n choom -n -600 -p "$PHASE_PID"` (children inherit; -600 not
+ -1000 — genuinely bigger consumers should still be reaped first). A phase
+ killed rc=143 with an earlyoom journal line naming a NEIGHBOR spike is the
+ collateral-kill signature: relaunch protected; on a SECOND kill despite
+ protection, route the phase to the cpu-bigmem/cpu-mid pod lane instead.

Scope / surfaces

• Primary target: .claude/skills/issue/SKILL.md
• Grep the workflow surface for the pattern before editing (grep -rln 'setsid nohup' .claude/ CLAUDE.md) and update every hit; list them in the plan (CLAUDE.md § vectorize bullet + .claude/rules/vectorize-many-cell-fits.md may carry sibling prose).

Constraints / invariants

• Workflow-surface only — never experiment code, configs/, or tasks/.
• scripts/workflow_lint.py --check-asks passes; ruff on touched files passes.
• This session runs under EPM_WORKFLOW_FIX_SESSION=1 and carries a workflow_fix_target: Provenance line — it MUST NOT auto-route any of its own subagents' workflow-fix candidates (recursion guard).

Provenance

• workflow_fix_target: .claude/skills/issue/SKILL.md
• fingerprint: 003f05f8de5e

Surfaced prose (orchestrator observation, task #811, 2026-07-03): earlyoom collateral kill of a detached VM-side fit phase; mitigated in-session with sudo choom -n -600; convention gap in the #833 detached-launch shape.