fix(hooks): CLAUDE_CODE_FORK_SUBAGENT is a feature flag, not a subagent marker — disables 9 hooks on every install - #1942
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settings.system.json sets CLAUDE_CODE_FORK_SUBAGENT=1 globally in env, because it is the feature-enable flag for forked subagents. isSubagentContext() also treated it as a runtime marker, so it returned true in EVERY session and all nine consumer hooks silently no-oped. Impact on a default install: memory review, memory injection, turn-start memory, delta surface, ISA sync, config-eval fire, system-change surface, and context loading all stop firing. Nothing errors; the affected state files just stop being written. A fork inherits its parent's environment, so the flag cannot distinguish a fork from its parent even in principle.
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Problem
settings.system.jsonsetsCLAUDE_CODE_FORK_SUBAGENT: "1"in the globalenvblock, because that variable is the feature-enable flag for forked subagents (per the Claude Code changelog: "Forked subagents can now be enabled on external builds by settingCLAUDE_CODE_FORK_SUBAGENT=1").hooks/lib/subagent.tsalso treats that same variable as a runtime marker identifying a subagent.Because the flag is set globally,
isSubagentContext()returnstruein every session, including the main one. All nine consumer hooks that gate on it silently no-op.Impact
On a default install, these stop firing entirely:
MemoryReviewFire,LoadMemory,MemoryTurnStart,MemoryDeltaSurface,ISASync,ConfigEvalFire,SystemChangeSurface,LoadContext,KittyEnvPersistNothing errors. The autonomic memory loop simply stops:
review-state.json,MEMORY/STATE/memory-inject, and the delta-surface heartbeat stop being written, while every hook not behind this guard keeps working normally. That asymmetry is the only visible symptom.Observed on a 7.40.4 install: the memory review loop was dead for five days before anyone noticed, and the hot layer stopped accumulating entries.
Why the flag cannot work as a marker
A forked subagent inherits its parent's environment. Even without the global
enventry, the flag would be present in both parent and fork, so it cannot distinguish them in principle.Fix
Remove
CLAUDE_CODE_FORK_SUBAGENTfrom the union inisSubagentContext(). The explicit markers (CLAUDE_AGENT_TYPE,CLAUDE_CODE_SUBAGENT_NAME,CLAUDE_CODE_SUBAGENT_TYPE,CLAUDE_AGENT_SDK, and the/.claude/Agents/path test) are unaffected.Trade-off
This removes the mitigation added for the fork double-context-injection issue referenced in the original comment. A fork may again re-inject main-session context. That is a duplicated context line; the current behaviour is a dead memory subsystem on every install. If fork detection is still wanted, it needs a marker the harness sets only in forks, which this flag is not.
Verification
With the flag removed,
isSubagentContext()returnsfalsein a main session, the Stop hook resumes writing per-session state andreview-state.json, and the reviewer fires on its normal cadence again.