Dual Build

/dual-build — parallel build with mandatory cross-review

This skill orchestrates a structured workflow that:

1. Splits a coding task into file-disjoint subtasks
2. Assigns roughly half to Claude and half to Codex
3. Runs all builders in parallel in isolated git worktrees
4. Has the OPPOSITE model review each diff (Claude reviews Codex's work; Codex reviews Claude's work)
5. Consolidates results and asks the user what to merge

The cross-review is the load-bearing piece. Different model families surface different classes of bug. The 50/50 split is a means to that end — you need both models to have produced something for both to be reviewable.

When to use

Use when the prompt has 2+ independently-scopable components AND quality matters more than raw speed:

• Multi-file feature spanning ≥3 files with clean module boundaries
• Batch of unrelated bug fixes
• Refactor with parallel slices (e.g., migrate N files to a new pattern)
• Audit-and-fix passes where cross-validation has real value

When NOT to use (bail criteria)

Bail (decline the workflow, recommend single-agent) if ANY of these hold. Bailing is a valid output of this skill — state the reason explicitly to the user, don't force-fit:

• Single-file or <150 LOC total delta across all subtasks. (Bumped from <50 in v0.2.3 after the 2026-05-06 bugfix-trio test run produced zero actionable cross-review findings on a 111-LOC 3-subtask split. Cross-review on small changes is theatre.)
• All subtasks are <40 LOC each. Even when total LOC passes the gate above, cross-review value is low if every individual diff is tiny. Median subtask size matters as much as total.
• All subtasks are "textbook fixes" — obvious patterns like adding validation, debouncing, timezone-aware date formatting, basic retry logic, simple encoding, dependency bumps, lint-rule conformance. Cross-review value is highest on subtle interactions and edge cases, not pattern-matching. If a builder could mechanically apply a textbook recipe, the reviewer is unlikely to find anything novel — confirmed by the bugfix-trio test run.
• Imbalanced split — any subtask is <20% of the total LOC delta. A 90/10 split passes "file-disjoint" but defeats the cross-review purpose: the reviewer of the trivial subtask has nothing to find, and the substantive subtask gets the same scrutiny as a single-agent run.
• Code-vs-docs ratio is heavy on docs. If half or more of the work is README / .env.example / CHANGELOG / setup prose, cross-review on docs is low-signal. Recommend single-agent for docs-heavy work.
• No file-disjoint decomposition possible — everything touches the same hot file. Worktree isolation can't help.
• Tightly-coupled work where every subtask needs every other subtask's output to test (cross-task dependencies > 1).
• Tightly-coupled-by-design components — even when file-disjoint, if the design decisions span all subtasks (e.g., "the renderer's behavior depends on the API's input-validation choices," "all three layers share an error-shape contract that's invented during the build"), single-agent context produces better cross-cutting decisions than coordinated agents working from a pre-written contract. Cross-review can catch decomposition damage but doesn't restore the cross-cutting design insight that was lost in the split. Pastebin's 2026-05-06 test run made this concrete: baseline shipped a generic JSON error handler, language-hint auto-fencing, a slug-shape guard, WAL journal mode, and a strict expires-in-hours allowlist — all cross-cutting decisions a single head naturally produced. Dual-build, working from a contract, missed those.
• Small fixture-scale tasks (~200 LOC) where each module's contract is locally specifiable AND the bug class is symmetric (one a single-agent would naturally avoid). Corrected after the v0.2.7 rerun: across 5 test fixtures run on 2026-05-06 (see EXAMPLES.md), two reproduced the "self-inflicted decomposition catch" pattern (#2 pastebin, #N3 recursive-to-iterative), and two produced clean dual-build wins (#3 callback-async-migration, #N2 audit-undisclosed-bugs) — both wins were timing/validation cases where the bug class was something single-agent would also miss. Bail on small file-disjoint refactors that are pure mechanical pattern-application; proceed if the work touches concurrency/timing/state-machine code or known-blind-spot validation patterns (see carve-outs below).

Positive-signal carve-outs (override the bail criteria above)

Even at low LOC or for tasks that look mechanical, cross-review value tends to be high when:

• Concurrency/timing/state-machine logic — throttle, debounce, retry, locks, queues, pollers. The 2026-05-06 test-04 retro proposed this carve-out after Codex's review caught a stale-timer bug in a Claude-built throttle that the existing test suite didn't pin. Sync-blocking, race windows, and reentrancy are exactly the kind of thing fresh adversarial eyes catch reliably.
• Validation logic where one model is known to have blind spots — e.g., typeof === 'number' && val > 0 letting NaN slip through (test-03's clean win). If the bug class is one a single agent would ALSO miss, cross-review pays off whether or not the codebase is large.
• Real-world large codebases where a single agent can't hold the whole problem in head — mission-control real-app cross-review catch (#1 in EXAMPLES.md) is the canonical example.
• Time-sensitive fixes — the workflow takes minutes, not seconds.
• Exploratory or interactive work — user is steering turn-by-turn.
• Working tree is dirty — uncommitted changes won't be visible to the worktrees (see prerequisites). Either commit/stash first or bail.

Required prerequisites

Run all of these checks before decomposing. If any fail, report and stop.

• Git repo: git rev-parse --is-inside-work-tree.
• Codex MCP healthy: mcp__codex__codex available and authenticated. Run /codex:setup if unsure.
• Worktrees feature available: git worktree list doesn't error.
• Clean working tree: git diff --quiet && git diff --cached --quiet. Worktrees branch from HEAD, so any uncommitted changes are invisible to the builders. If dirty:
  • Surface the situation to the user.
  • Ask them to either commit the WIP as a checkpoint commit (git commit -am "wip: pre-dual-build checkpoint") or explicitly acknowledge the WIP won't be in the worktrees.
  • Do not silently git stash and pop — that introduces a parallel failure mode if subtasks touch the same files.
• Capture parent HEAD SHA: before any worktree dispatch, run git rev-parse HEAD and save the output. This is the expected base for every worktree (verified in Stage 1.5).

Pipeline

Stage 0 — Decompose

Read enough code (Glob, Grep, targeted Reads) to understand the module boundaries the task touches. Then produce a task split with these properties:

• 2–6 subtasks total. Fewer is fine; more than 6 means the task is probably too granular and overhead will dominate.
• File-disjoint. No two subtasks may touch the same file. If two pieces of work touch the same file, merge them into one subtask. If you cannot achieve disjoint scopes, bail out.
• Balanced. No subtask should be <20% of the total estimated LOC delta. If your decomposition is lopsided (e.g., 3 bugs in one file + 1 line in another), the right answer is single-agent — bail.
• ~50/50 assignment between Claude and Codex. Don't agonize over the split; roughly even is fine. Slight preferences:
  • Codex tends to be strong at scaffolding, boilerplate, and well-specified mechanical changes
  • Claude tends to be strong at nuanced refactors and reasoning-heavy changes
  • But these are weak heuristics; if in doubt, alternate assignments

Each subtask must specify:

• id — short identifier (T1, T2, T3, …)
• assigned_to — "claude" or "codex"
• goal — one sentence
• brief — 2–4 sentences of implementation guidance
• file_scope — explicit list of paths the subtask may touch
• acceptance — how to verify (tests, build, behavior)

Show the split to the user and wait for confirmation before dispatching builders. If they redirect (reassign tasks, adjust scope, add/remove a subtask), accept and re-plan. Do not proceed without explicit go-ahead — the parallel build phase will spawn N agents and is non-trivial to abort cleanly.

Auto-approve mode (unattended runs): if the env var DUAL_BUILD_AUTO_APPROVE=1 is set (check with Bash(echo "${DUAL_BUILD_AUTO_APPROVE:-0}")), skip the user-confirmation pause. Write the proposed split to _dual-build-plan.md in the working directory for asynchronous review and proceed directly to Stage 0.5 (then Stage 1). Use only for unattended/benchmark runs (e.g., the test harness in the repo's test-suite/). Interactive use should keep the pause — the pause exists for a reason.

Stage 0.5 — Cross-cutting alignment doc

After the user confirms the split (or auto-approve fires), write a short _dual-build-decisions.md to the working directory listing cross-cutting choices that all builders should converge on. This pre-empts the "self-inflicted decomposition catch" pattern observed across 3 of 5 test fixtures (pastebin, test-04, test-05) where isolated builders made different implementation choices for the same kind of decision and the workflow paid for cross-review to find the divergence.

Examples of cross-cutting decisions worth pinning:

• Validation patterns — e.g., use Number.isFinite() for numeric checks, not typeof === 'number' (which lets NaN through)
• Error shapes — which error class, which message format (especially when modules document contracts like Error('opts.timeoutMs must be positive number'))
• Iteration / data-structure conventions — e.g., for sparse arrays, use Object.keys() to skip holes naturally
• Resource cleanup — always use try/finally to release X, or prefer AbortController over manual cleanup flags
• Naming and import conventions — helpers go in lib/utils.js, tests in test/<module>.test.js not tests/

Generate this doc by re-reading the per-task briefs from Stage 0 with an eye toward "if I were writing all four tasks myself, what choices would I make consistently?" The point is to surface the implicit decisions a single-agent builder would make naturally, so isolated builders can match them.

Length: ~5–25 lines, bullet-form. Short. If you genuinely can't identify any cross-cutting concern (truly independent modules, no shared patterns), write (no cross-cutting concerns identified — modules are independent in style) so the file's presence documents that no shared decisions were necessary. An empty / missing decisions doc is the failure case from earlier versions of the workflow.

Hard constraint (v0.2.8): only encode decisions the contracts strictly require

The alignment doc is structurally dangerous — opinionated choices propagate to all builders consistently, so wrong choices ship as cross-cutting regressions. Test-05's v0.2.7 rerun made this concrete: the orchestrator wrote §6: "treats shared-reference DAGs as cycles too. That's acceptable: the contract says 'no shared references with the input' in the output" — but the contract said "throw on cycles", not "throw on DAGs". All four builders honored the wrong decision; the recursive baseline naturally cloned DAGs correctly. Cross-review caught the regression, but the orchestrator then failed to apply the fix and shipped the bug.

Rule: include a decision in _dual-build-decisions.md ONLY if it is:

1. Forced by the contract — e.g., the file says "throws Error('cyclic reference')" so error message text is locked.
2. Forced by the project's existing code — e.g., package.json declares "type": "module" so ES modules are mandatory; existing tests use node:test so the test runner is locked.
3. Forced by an explicit user instruction in the task brief — e.g., "use AbortController for timeouts".

DO NOT include opinionated cross-cutting choices that diverge from what a single-agent reading the same brief would naturally choose. If you're tempted to write "this is acceptable because [pragmatic argument]" or "the test suite doesn't exercise this", that's the signal to STOP and remove the decision rather than encode it. The single-agent baseline isn't constrained by the doc you're writing — and if it would naturally make a different choice, that's the choice to default to.

When in doubt, leave the decision OUT. Builders making slightly different but locally-correct choices is recoverable via cross-review (sibling-diff context exists for this). Builders making consistently-wrong choices because the orchestrator told them to is NOT recoverable — cross-review can flag it but the orchestrator may then fail to apply the fix (test-05 v0.2.7).

This stage is mandatory but the doc may be near-empty. Empty-but-present (just the file with (no cross-cutting concerns identified)) is strictly better than encoding speculative decisions.

Stage 1 — Parallel build

Once the user confirms the split, dispatch all builders in a SINGLE message with N parallel Agent tool calls.

For each subtask assigned to Claude:

Agent(
  subagent_type: "claude-builder",
  isolation: "worktree",
  description: "Build T<id>: <one-line goal>",
  prompt: "<full structured brief — Task ID, Goal, Brief, File scope, Acceptance, Project notes, plus 'Parent HEAD: <PARENT_HEAD_SHA>. Verify with `git log --oneline -3` and report the output in your final report.' AND 'Cross-cutting decisions: read _dual-build-decisions.md in the working directory before starting and honor those choices.'>"
)

For each subtask assigned to Codex: same shape, subagent_type: "codex-builder".

Embed the parent's HEAD SHA in every brief. This lets builders self-check their base and gives the orchestrator data to detect mismatches in Stage 1.5.

Embed the cross-cutting decisions reference in every brief. Builders must read _dual-build-decisions.md from the working directory before implementing. This is the load-bearing piece that prevents the self-inflicted decomposition pattern.

Wait for all to return. Each response includes the worktree path, branch name, files changed, and a structured report.

Stage 1.5 — Verify worktree bases

This is the single most important post-dispatch check. Before proceeding to Stage 2, verify each worktree was rooted at the parent's HEAD. Worktrees occasionally default to main / HEAD-of-default rather than the working branch's tip, which silently invalidates the entire run (builders target outdated symbols, diffs don't merge cleanly, reviewers chase phantom conflicts).

For each builder report:

1. Each builder's report includes a git log --oneline -3 output. Read it.
2. The third commit in that listing (the worktree's base before the builder's commits) should equal the parent HEAD SHA captured in prerequisites.
3. Cross-check: git -C <worktree_path> merge-base HEAD <parent_head_sha> must equal <parent_head_sha> exactly. (Parent HEAD must be an ancestor of the worktree's HEAD.)

If a base mismatch is detected for subtask T:

• Do not proceed to cross-review for that subtask. The reviewer will chase phantom issues.
• Surface to user: "Worktree T was rooted at instead of expected . Builder may have targeted symbols that don't exist on the working branch. Recommend: re-rebase the worktree onto current HEAD and re-run that builder, OR abandon this subtask."
• Wait for user decision before continuing.

This single check would have prevented the entire FinancialResearch run failure (2026-05-05) where every worktree was rooted at a stale base.

Stage 1.6 — Orchestrator commits Codex builder's edits (always)

As of v0.2.4, codex-builder agents do NOT attempt git commit themselves — the failure mode is reliable enough across runs (SecureCatch, mission-control, bugfix-trio, pastebin all hit it; pastebin had 2/3 builders fail) that preempting the attempt is cleaner than recovering from it. The orchestrator handles the commit step routinely.

For each subtask whose builder is codex-builder:

1. The builder's report includes its git status --porcelain output and the commit message it would have used (status: "Done — edits applied, awaiting orchestrator commit").
2. Spot-check one changed file with Read to confirm edits match the builder's reported summary.
3. Run the commit:

   git -C <worktree_path> add -A
   git -C <worktree_path> commit -m "<message from builder report>"
   

4. Continue to cross-review.

For claude-builder agents, the builder commits itself — no orchestrator commit step needed.

If a codex-builder somehow returns a successful git commit -h <sha> reference (rare, but possible if the sandbox ever permits writes), skip step 3 — the commit already exists.

Stage 1.7 — Run tests in each worktree (pre-review verification)

Before dispatching reviewers, run the project's test command in each worktree from the orchestrator. This gives every reviewer the same verified ground truth and catches builder acceptance-claims that don't survive the test suite.

For each subtask's worktree:

1. Detect the test command. Heuristic order: npm test if package.json has a non-default test script; else node --test if *.test.{js,mjs} files exist; else pytest if pyproject.toml/pytest.ini/tests/; else skip with a note.
2. Run from the orchestrator: git -C <worktree_path> ... or cd <worktree> && <test_cmd>. Capture pass/fail + last ~30 lines of output.
3. Include the result in the reviewer's brief as Pre-review test result: PASS/FAIL plus the captured output.
4. If a worktree's tests FAIL but the builder's report claimed acceptance passed, that's an automatic Important finding ("acceptance honesty") — the orchestrator should record it before dispatching the reviewer.

Why centralize test execution in the orchestrator: Codex reviewers run in read-only sandbox and cannot execute tests; Claude reviewers can but shouldn't run tests redundantly across N parallel reviewer dispatches. Centralizing gives every reviewer the same verified ground truth and the result is included in their brief.

Shared-test-file deletion gotcha

If any subtask owns the deletion of a shared test file that imports the OLD API of all modules (e.g., a baseline.test.js written against pre-migration callback signatures), the other subtasks' worktrees will hang or fail when the full test suite runs — they migrated their own module to the new API but still have the old shared test file pointing at every other (still pre-migration in their worktree) module. The whole-suite test run hangs on never-firing callbacks or fails on signature mismatches, which is a misleading signal: the per-module changes themselves are fine.

Detection: if Stage 1.7 reports a hang or full-suite FAIL in N-1 of the N worktrees while the Nth worktree (the one owning the deletion) passes, that's the pattern.

Workaround: in those N-1 worktrees, run only the per-task test file (node --test test/<module>.test.js or equivalent) and pass that PASS/FAIL into the reviewer brief. Note in the brief that the full-suite hang/fail was a known cross-task isolation artifact, not a real regression. The merged result will exercise the full suite cleanly post-merge — that's the post-merge verification step.

Surfaced by the 2026-05-06 callback-async migration test fixture (test-03). See EXAMPLES.md #3.

Stage 1.8 — Per-task failure handling

• Builder returns Blocked or errored: do NOT cancel the others. Report after all builders finish; ask whether to abort, retry that subtask, or proceed without it.
• Codex 5xx or AnyIO timeout <60s: retry the builder ONCE before escalating. These are usually transient API issues.
• ❌ Codex handoff failed: the worktree may exist but be empty. Do NOT auto-retry on auth-related errors (401/403/expired token). Report and stop.

Stage 2 — Parallel cross-review

Before dispatching, capture each task's diff so each reviewer can see siblings' implementations:

for each completed worktree W with branch B:
  sibling_diff[B] = `git -C <W> diff <PARENT_HEAD>..HEAD`

Cap each sibling diff at ~500 lines (truncate with head -500 plus a ... [truncated] note); 4 siblings × 500 lines is a workable context budget.

Dispatch all reviewers in a SINGLE message with N parallel Agent calls. Critical: each task is reviewed by the OPPOSITE model. Claude-built tasks → codex-reviewer; Codex-built tasks → claude-reviewer.

Each reviewer brief must include a Sibling diffs section listing the OTHER tasks' diffs (everything except the diff being reviewed). This lets the reviewer:

• Spot cross-cutting asymmetries — e.g., "Sibling T1 uses Number.isFinite() for numeric validation; this task (T3) uses typeof === 'number', which lets NaN through." The 2026-05-06 test-03 + test-04 + test-05 runs all surfaced bugs of this exact shape; injecting sibling diffs lets the reviewer flag the divergence directly rather than merely catching the bug after-the-fact in isolation.
• Cross-check shared utilities — if T1 and T3 both implement an "is positive number" check inline, the reviewer should suggest extracting a shared helper rather than letting the inconsistency ship.

The sibling diffs are read-only context for the reviewer, not the artifact under review. The reviewer must NOT comment on the sibling code itself or assert that something in a sibling is broken (that's the sibling reviewer's job, and the cross-task-wiring rule from v0.2.4 still forbids "X is unused / Y is missing" claims about sibling worktrees). They CAN say "T handled this differently — consider aligning."

Reviewers do NOT use isolation: "worktree" — they read the existing builder worktree directly via git -C <path> and the Read tool with absolute paths.

Single auto-retry on transient errors (HTTP 5xx, AnyIO timeout <60s with no useful output) before escalating.

Wait for all reviews. Each returns severity-tagged findings (Critical / Important / Praise) and a recommendation (Ready / Fix-before-merge / Rework).

Cross-review depth + verification

Reviewer findings can be confidently wrong — a past run had a Codex reviewer declare JIRA_CSIRT_EMAIL "referenced nowhere in the codebase" when it was actively used in lib/jira.ts:46-48. Don't apply findings blindly:

• Spot-check Critical and Important findings against ground truth before applying. Especially negative claims ("X is unused", "Y has no callers", "Z is dead code") — a 30-second grep -r '<symbol>' . saves applying a hallucinated finding.
• Note review depth asymmetry: Codex reviews on past runs have been substantially lighter than Claude reviews (4 praise bullets vs. paragraph-per-finding with file:line citations). If Codex's review of a Claude-built diff produces only "looks good" findings, prompt yourself: did the reviewer actually engage with edge cases? Sometimes the answer is "the diff really is clean"; sometimes the answer is "rerun with explicit edge-case prompting."

Stage 3 — Consolidate & report

Produce a unified report grouped per task. For each task:

## T<id> — <goal>
**Assigned**: claude | codex
**Builder status**: Done | Done with caveats (commit recovered) | Blocked
**Worktree base**: ✅ matches parent HEAD | ❌ stale (T<id> excluded from review)
**Reviewer recommendation**: ✅ Ready / ⚠️ Fix Important / ❌ Rework

**Build summary** (from builder report): …
**Cross-review** (from reviewer): …
  - Critical findings: …
  - Important findings: …
  - Praise: …
**Verification spot-checks** (any reviewer claims you grep-verified): …

Then a top-level summary:

• Total tasks, ready vs. needs-rework count, any excluded due to base mismatch
• Cross-task issues you noticed (overlapping logic, contradicting assumptions, etc.) — these are things only the orchestrator can see
• Recommended merge order if some tasks depend on others

Stage 4 — Apply or abandon

Do NOT auto-merge. Merging into the main checkout is a destructive operation that needs user confirmation. Present the consolidated report and ask for per-task decisions:

• Merge: git merge --no-ff <branch> (or --squash, per user preference) into the main checkout. Resolve conflicts if any (typically there should be none, since file_scopes were disjoint — if there are conflicts, surface them rather than silently resolving).
• Rework: leave the worktree and branch in place; the user may iterate.
• Abandon: git worktree remove <path> then git branch -D <branch>. Confirm with the user before deleting work.

Worktree cleanup gotcha

git worktree remove may fail with "cannot remove a locked working tree, lock reason: claude agent agent-… (pid …)". The Agent system locks worktrees while an agent task is "live" and doesn't auto-unlock when the task returns. Don't reach for -f -f — just unlock first:

git worktree unlock <path>
git worktree remove <path>

Post-merge verification

After merges complete, run the project's test suite (npm test, pytest, etc.) yourself in the main checkout. Reviewers are read-only and may not have been able to execute the full suite — the orchestrator is the final test-running step. If tests fail post-merge, you have a real signal that the cross-review missed something or the merges interacted unexpectedly.

Then ask whether to clean up remaining worktrees (run the unlock+remove sequence per worktree).

Cleanup of Stage 0.5 / 0 plan files

Once merges are complete (or work is abandoned), remove the orchestrator-generated plan files from the working directory:

• _dual-build-plan.md (auto-approve only — written in Stage 0)
• _dual-build-decisions.md (always — written in Stage 0.5)

These are scratch artifacts; they should not be committed.

Guardrails

• Bail criteria are strict. Re-read "When NOT to use" if Stage 0 produces an imbalanced or docs-heavy split — single-agent is the right tool more often than the workflow's framing suggests.
• Worktree base verification is mandatory. Stage 1.5 catches a real failure mode that has invalidated entire runs. Never skip it.
• No auto-merge without user confirmation per task.
• No auto-cleanup of worktrees or branches without confirmation. The user might want to inspect them.
• The cross-review is mandatory. If a reviewer fails, retry it once; if it still fails, report the gap to the user — do not skip the review and recommend merge.
• Reviewer findings need spot-checks. Confidently-wrong findings have shipped. Verify Critical/Important claims with grep or Read before applying.
• Orchestrator runs the post-merge tests. Reviewers can't always execute the suite; you're the final check.

Cost note

A typical run is: N builder invocations (Opus + Codex) + N review invocations (Codex + Opus) + orchestrator overhead. For N=4 that's ~8 model calls plus the orchestrator's planning. Budget several minutes wall time and meaningful token spend.

The cross-review is what justifies the cost. On runs with substantive findings (e.g., race-condition catches, edge-case discoveries), it earns its keep. On runs with no findings — or with all findings being false positives — it's overhead. Bail criteria exist to avoid those runs.

Changelog

v0.2.8 (2026-05-06) — corrections + v0.2.7 rerun findings.

• Corrected the test-04 misclassification. The original v0.2.4 analysis used a 2-call probe that didn't trigger the throttle bug; the v0.2.7 rerun's LLM judge ran the dual-build's regression test against baseline and confirmed [a, c, b] instead of [a, b, c]. Both v0.2.4 and v0.2.7 baselines ship the throttle stale-timer bug. Test-04 is now correctly classified as a clean dual-build win alongside test-03. Self-inflicted-decomposition pattern now reproduces across 2 of 5 fixtures (pastebin, test-05), not 3 of 5.
• Hard constraint added to Stage 0.5 alignment doc. The orchestrator must include only decisions strictly required by the contracts, the existing project code, or explicit user instructions — no opinionated cross-cutting choices that diverge from natural single-agent behavior. Test-05's v0.2.7 rerun made this concrete: the orchestrator wrote §6: "treats DAGs as cycles too", the wrong-but-encoded choice propagated to all builders, cross-review caught the regression, and the orchestrator then failed to apply the fix — bug shipped. "When in doubt, leave the decision OUT" is the rule.
• EXAMPLES.md updates: corrected #N2 framing (clean win), added v0.2.7 rerun results to both #N2 and #N3, updated the Pattern observation count.

v0.2.7 (2026-05-06) — two structural changes targeting the "self-inflicted decomposition catch" pattern observed across 3 of 5 fixtures (pastebin, test-04, test-05). Both changes try to prevent the divergence at source rather than catching it late.

• New Stage 0.5 — Cross-cutting alignment doc. After Stage 0's task split is confirmed, the orchestrator writes _dual-build-decisions.md listing cross-cutting choices (validation patterns, error shapes, iteration conventions) all builders must converge on. Builders read it before implementing. Both claude-builder and codex-builder agents updated to require this read step. Cleanup added to Stage 4.
• Sibling-diff injection in Stage 2. Reviewers now receive the OTHER tasks' diffs (capped ~500 lines each) as read-only context. New responsibility: flag cross-cutting asymmetries (e.g., "T1 uses Number.isFinite, T3 uses typeof === 'number' — NaN slips through here") as Important findings. Both claude-reviewer and codex-reviewer agents updated. The cross-task-wiring rule (forbidding "X is missing"-style claims) is preserved with a sharpened distinction: pattern asymmetry between two diffs you can read = ✅ flag; wiring claim about post-merge behavior = ❌ still forbidden.

These two changes are untested as of this commit — they're skill-doc + agent-prompt updates, no executable code. The next test-suite sweep will measure whether they reduce the self-inflicted-catch rate. Hypothesis: test-04 and test-05 (small fixture-scale, locally-specifiable contracts) should now produce zero asymmetry-class findings rather than the ones they shipped pre-fix; whether that translates to real cost-benefit improvement depends on whether the alignment doc + sibling diffs add enough overhead to outweigh the saved review-then-fix cycles.

v0.2.6 (2026-05-06) — based on test-04 (audit of utility modules) + test-05 (recursive→iterative migration) A/B runs. Both produced "baseline better" verdicts for the same reason: cross-review caught real bugs, but the bugs only existed because dual-build's decomposition introduced them; single-agent baseline naturally avoided them. The pattern is now reproducible across 3 of 5 fixtures (pastebin, test-04, test-05).

• New bail criterion: small fixture-scale (~200 LOC) file-disjoint refactors where each module's contract is locally specifiable. Expect "self-inflicted decomposition catch" rather than real lift over baseline.
• New positive-signal carve-outs: concurrency/timing/state-machine logic (throttle, debounce, retry, locks, queues), validation logic with known model blind spots (NaN-style), and real-world large codebases where single-agent context can't hold the whole problem. Cross-review value is high in these regardless of LOC.
• EXAMPLES.md updates: new #N2 audit-undisclosed-bugs and #N3 recursive-to-iterative entries under "Negative results", plus a top-level "Pattern observation" section documenting the self-inflicted-decomposition catch pattern across 3 of 5 fixtures.

v0.2.5 (2026-05-06) — based on the test-03 callback→async/await migration A/B run, which produced the test suite's first "dual-build clearly better" LLM-judge verdict (cross-review caught a NaN validation bug that single-agent baseline shipped + zero NaN tests):

• Stage 1.7 — shared-test-file deletion gotcha: documented the hang/fail pattern when one subtask owns the deletion of a shared test file. N-1 sibling worktrees see hangs or signature-mismatch failures during the full-suite run; workaround is to run only the per-task test file and note the cross-task isolation artifact in the reviewer brief. Surfaced by test-03 where T1 owned the deletion of test/baseline.test.js (which imported all four callback APIs).
• EXAMPLES.md updated: new Section 1 entry #3 — callback → async/await migration test fixture with the NaN-validation cross-review catch, the 2-line node -e post-deploy exploit demonstration, and calibration findings (baseline auto-invocation suppression, shared-test-file gotcha, cross-review depth asymmetry continues but doesn't predict who catches the bug).

v0.2.4 (2026-05-06) — based on the pastebin test-suite run that produced a real cross-review catch (Express default-error-handler stack-leak in dev mode) and surfaced two structural improvements:

• Reviewers must NOT assert on cross-task wiring. A reviewer only sees one task's isolated worktree; sibling tasks aren't merged in. Pastebin's T2 reviewer falsely claimed cleanupExpired() was never called when it actually lives in T1's worktree. Reviewer prompts now explicitly forbid this — surface as "Cross-task contract — orchestrator spot-check on merge" instead of Critical/Important.
• codex-builder no longer attempts git commit at all. The read-only-fs failure has now hit 4+ runs reliably (SecureCatch, mission-control, bugfix-trio, pastebin). Codex builders stop after edits, include their intended commit message in the report, and the orchestrator commits on their behalf as a routine step (not a "recovery path"). Stage 1.6 reframed accordingly.

v0.2.3 (2026-05-06) — based on the bugfix-trio test-suite run that completed acceptance with zero actionable cross-review findings:

• Bail threshold: <50 LOC bumped to <150 LOC total. Three textbook bugs at 111 LOC total passed all checks but the run produced no Critical/Important findings — the threshold was too generous.
• Added per-subtask floor: <40 LOC per subtask → bail. Median size matters as much as total.
• Added "textbook fixes" criterion: even at sufficient LOC, cross-review value is low when bugs follow obvious recipes.
• Added Stage 1.7: orchestrator runs the project's test command in each worktree before dispatching reviewers and includes the result in every reviewer's brief. Codex reviewers run in read-only sandbox and can't execute tests; this centralizes the verification step. Builder-claims-pass + pre-review-fails is automatically Important.

v0.2.0 (2026-05-06) — based on four real test-run retrospectives across user projects (OSINT-Extension, FinancialResearch, SecureCatch, mission-control):

• Add Stage 1.5: post-dispatch worktree base verification (FinancialResearch run had every builder rooted at a stale commit, invalidating the whole pipeline).
• Add Stage 1.6: documented Codex-builder partial-success recovery (recurring "files-on-disk-but-uncommitted" mode in SecureCatch + mission-control runs).
• Add git worktree unlock cleanup step (mission-control run hit this).
• Add clean-tree precondition (worktrees-branch-from-HEAD invariant).
• Tighten bail criteria: balance check (<20% subtask), code-vs-docs threshold, hard <50 LOC threshold (OSINT-Extension run correctly bailed; criteria now codify why).
• Add single auto-retry on transient builder/reviewer errors.
• Embed parent HEAD SHA in builder briefs so builders can self-check base.
• Add cross-review depth + spot-check guidance (SecureCatch run had a Codex reviewer hallucinate a negative claim about JIRA_CSIRT_EMAIL).

v0.1.0 (2026-05-05) — initial release.