Codex re-fires SessionStart with source "compact" after every context compaction; the summary keeps progress but sheds the bootstrap and any active skill's instructions — measured July cause of post-compaction dispatch drift in long SDD runs (with re-injection: 18/18 hook fires, 66/66 post-compaction dispatch tuples correct in a 12.4h stress run). Codex discovers skills natively at startup, so the hook is silent there: the compact re-fire is the one unowned lifecycle point. Adds the plugin-provided hook (hooks-codex.json + session-start-codex, compact-only, fails open), wires it into the manifest and package, documents install/trust behavior, updates codex-tools.md with the re-grounding fallback, and tests the hook lifecycle, manifest, and archive contents. Rebuilt from the July codex-spinout-fixes branch, pared to the hook core: the dispatch-hints layer it used to ride with is superseded by the merged 2059-2062/2077-2080 stack and is dropped. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Subagent dispatch requires multi-agent support
Add to your Codex config (~/.codex/config.toml):
[features]
multi_agent = true
This enables the multi-agent tools that skills like
dispatching-parallel-agents and subagent-driven-development use.
Which tools you get depends on the multi-agent version your model
preset selects (current presets run V2; older ones run V1). Trust your
actual tool list over any table — including this one — when they
disagree.
- Spawning: give children a clean context with
spawn_agent {fork_turns: "none"}; the default"all"copies your entire transcript into the child. On Codex 0.145+, role files under~/.codex/agents/attach to isolated forks viaagent_type. Full-history forks acceptmodelandreasoning_effortoverrides (onlyagent_typeis refused there) — isolated forks are the SDD default for context hygiene, not because overrides require them. - Fix rounds: resume the implementer with
followup_task— it delivers your message, triggers a turn, and transparently reloads a child the harness evicted. Never dispatch a fresh implementer on the theory that a spawned agent cannot be messaged again; on V2 it always can. - Lifecycle: V2 has no
close_agent. Finished children are evicted automatically when slots are needed; leaving them unclosed costs nothing. Only V1 sessions haveclose_agent— there, close reviewers when their review returns, and close each implementer after its task's review passes. - Model names: never copy a model name from a skill, table, or old
session into
spawn_agentwithout checking it against your current spawn allowlist — V2 accepts only V2-capable presets and hard-errors on the rest.
Waiting on children
wait_agent is an event subscription, not a poll: a long wait wakes
the moment a child produces mailbox activity, with the same latency as
a short one. Short-timeout polling buys nothing and costs a tool call —
and a context rebill — per poll. In measured sessions, roughly
two-thirds of all wait calls were short polls that timed out.
- While you still have local work, do not wait at all. A completed child's final answer is pushed into your mailbox and arrives with your next turn.
- When you are genuinely idle with children outstanding, wait in
bounded stretches:
wait_agentwithtimeout_ms300000-600000 (5-10 minutes). After each stretch — wake or timeout — post one status line, runlist_agents, and chase any child that finished without reporting. Never stack polls shorter than five minutes; the event subscription wakes a bounded stretch just as fast as a short one. - Completion mail cannot wake an idle controller (it is delivered
without triggering a turn); covering that idle window is
wait_agent's only job. A stretch that times out with no activity is your cue to reconcile, not to shorten the next stretch.
Model routing on spawns
Every spawn_agent you issue — including when you are yourself a
spawned child running a fan-out — sets model AND reasoning_effort
explicitly, per the Model Selection rules of the skill you are
executing. Setting model alone is a trap: the child's effort
silently resets to that model's default, not to yours.
Ask your human partner to add a machine-level backstop to
~/.codex/config.toml so any spawn that slips through still routes to
a deliberate tier instead of silently inheriting the session's most
expensive model:
[agents]
default_subagent_model = "<a mid-tier model from your spawn allowlist>"
default_subagent_reasoning_effort = "medium"
Compaction sheds these instructions
Context compaction replaces your transcript with a summary that keeps
your progress but not your working instructions — the first
post-compaction dispatch is where routing drift starts, and once one
bare spawn lands, the broken pattern becomes its own precedent. The
plugin ships a compaction re-injection hook (hooks/hooks-codex.json,
Codex 0.145+) that restores the bootstrap after every compaction; it
needs one-time trust approval, so if you never see a
<CONTEXT_RESTORED> block after a compaction, tell your human partner
the hook may be untrusted or unsupported on this version. Without it,
re-ground yourself: when a summary appears in your context, re-read
this file and the SKILL.md of the skill you are mid-way through
executing before your next dispatch, and trust the ledger over your
summarized memory of what happened.
Environment Detection
Skills that create worktrees or finish branches should detect their environment with read-only git commands before proceeding:
GIT_DIR=$(cd "$(git rev-parse --git-dir)" 2>/dev/null && pwd -P)
GIT_COMMON=$(cd "$(git rev-parse --git-common-dir)" 2>/dev/null && pwd -P)
BRANCH=$(git branch --show-current)
GIT_DIR != GIT_COMMON→ already in a linked worktree (skip creation)BRANCHempty → detached HEAD (cannot branch/push/PR from sandbox)
See using-git-worktrees Step 0 and finishing-a-development-branch
Step 1 for how each skill uses these signals.
Codex App Finishing
When the sandbox blocks branch/push operations (detached HEAD in an externally managed worktree), the agent commits all work and informs the user to use the App's native controls:
- "Create branch" — names the branch, then commit/push/PR via App UI
- "Hand off to local" — transfers work to the user's local checkout
The agent can still run tests, stage files, and output suggested branch names, commit messages, and PR descriptions for the user to copy.