c97988d8d1
Codex SDD runs at frontier tiers spin out: subagents inherit the session's model and effort, review seats find real-but-endless defects every round, and the final whole-branch review has no reachable termination state. Field forensics across multiple real sessions traced the mechanism: spawn_agent's fork_turns defaults to "all" (full-context forks that also refuse model overrides), omitted model/effort params inherit the frontier parent, and dispatch rules loaded at session start do not survive context compaction — a compacted controller reverts to inheritance exactly when the session is longest and most expensive. Three coordinated changes: - codex-tools.md: every SDD spawn sets fork_turns "none" plus explicit model/reasoning_effort when the schema supports them (Codex 0.145+), with an inheritance warning for older builds; reviewer tier never exceeds implementer tier and fix rounds never get effort bumps. - task-brief/review-package print a dispatch tuple with their output (review-package grows --role for re-review/final-review), putting the routing values in front of the controller at the moment of dispatch — reprinted every round, so they survive compaction by construction. - SKILL.md: the final-review wave closing is policy, not a verdict — one fix dispatch, one scoped re-review, residuals adjudicated to the ledger; one-off review procedures never become standing; Model Selection defers to platform role tables where one exists. Validated live: a previously spun-out 14-task run (8h, 6 tasks, died mid-loop) re-executed to completion under these changes — bounded fix loops, single-cycle final review, ~20 consecutive correctly-routed dispatches across two compactions. Reviewer-tier matrix (125 cells) showed no calibration cost: clean-diff approvals and planted-defect recall are identical across tiers. Eval scenarios to follow before any upstream submission. 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 spawn_agent, wait_agent, and close_agent for skills like dispatching-parallel-agents and subagent-driven-development. When using subagent-driven-development, close reviewer subagents when their review returns. Keep each implementer subagent open until its task's review passes — the fix loop resumes the implementer — then close it. If your harness cannot send another message to a spawned agent, dispatch each fix round as a fresh implementer carrying the brief, the report file, and the findings.
SDD dispatch: pin fork_turns and the model on every spawn
Every spawn_agent call in subagent-driven-development sets
fork_turns: "none". The parameter defaults to "all", which forks your
entire session transcript into the child — the opposite of the fresh,
constructed context SDD requires — and a full-history fork also refuses
model and effort overrides. Never omit the parameter, and never pass
"all" or a turn count for an SDD dispatch.
Before Task 1, check your spawn_agent tool schema for model and
reasoning_effort parameters (present on Codex 0.145+).
If the parameters exist, set both explicitly on every dispatch. The
task-brief and review-package scripts print the exact values for each
dispatch as a dispatch (codex spawn_agent): line with their output —
copy that line's values onto the spawn_agent call verbatim, every time,
even late in a long session. The mapping they print: every SDD seat runs
gpt-5.6-terra — implementers and reviewers at reasoning_effort: high,
scoped re-reviews at medium. On Codex this mapping IS the Model
Selection section — including the final review, which stays on
terra/high rather than "most capable available." Never give a subagent
your session's model when you run a frontier config (sol at xhigh or
max): reviewer tier never exceeds implementer tier, and a fix round
never gets an effort bump. Rounds 4-5's "more capable model" means a
fresh implementer at the same tier; a task that genuinely needs more
than terra/high is a BLOCKED escalation to your human partner, not a
quiet tier climb. Inherited frontier-tier subagents are a measured cause
of SDD runs spinning out for hours: review seats that inherit a frontier
model at maximum effort find real-but-endless defects every round, and
fix diffs balloon instead of converging.
The model names here track Codex's spawn_agent allowlist (currently
gpt-5.6-sol and gpt-5.6-terra). When the allowlist changes, update
this file and the hint lines in task-brief and review-package together.
If the parameters do not exist (Codex 0.144 and earlier), every child
inherits your session's model and effort and no override is possible —
role files in ~/.codex/agents/ do not attach to spawns either. Say so
to your human partner before starting a plan of more than a few tasks,
and offer the choice: proceed with inheritance, or restart the session
at a lower effort so the whole run — controller and children — pays the
lower rate.
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.