[JacobStephens2]

Summary

A Command's sessions run on a Harness (claude or codex), with a Model and an Effort, chosen on the command line, then the User config, then the default (claude, and the Harness's own Model and Effort).

thirdshift <issue-url> harness codex model GPT-6.1-Sol effort Max
  Choice::of(command, User config)          # command > [harness.<name>] > default
  check before work                         # before the Claim, worktree, any log
    CLI on PATH
    codex: match against `codex debug models` (case-insensitive, display name → slug)
    claude: test call, only when a Model is named
  Spec run / Pass: check once, after deciding not to skip
  every session (implement, Repair, Resume, Spec review, Architecture review,
                 Ticket Runs, Base fix) → same Choice via child-Run args
  record: Command log, Activity log, PR body "Built with …", Run notification

[harness]           default = "claude" | "codex"
[harness.claude]    model, effort     # blank: Claude Code's own default
[harness.codex]     model, effort

The Factory skills stop being a Claude plugin (ADR 0012):

-skills/<skill>/            loaded with claude --plugin-dir, as /thirdshift:<skill>
+skills/thirdshift-<skill>/ linked into the worktree, kept out of git by .git/info/exclude
+  claude → .claude/skills/   prompt's first line: /thirdshift-<skill>
+  codex  → .agents/skills/   prompt's first line: $thirdshift-<skill>

A Codex session runs codex exec --json --dangerously-bypass-approvals-and-sandbox with stdin null, -m / model_reasoning_effort, and the CLAUDE.md fallback. Its stream gives the progress lines, Session log, thread id and final message. A Resume runs codex exec resume <thread> with every flag again. A command or sub-agent call left running gets one Resume, turn.failed fails the Run with Codex's error, and an interrupt sends SIGINT before SIGTERM.

Setup asks for the Harness. Both are listed, and one that isn't installed is marked and refused. The default answer is the configured Harness if it's installed, otherwise the installed one, so claude when both are. Setup then asks the Model and Effort for that Harness only. For Codex it lists them from Codex's catalog, and it checks each answer the way a Run does.

Review clean-ups in the last commit:

• The headless and Resume lines no longer name Claude's Bash timeout or TaskStop tool unconditionally.
• Re-running Setup keeps a configured codex as the default answer.

Evidence

• Before: tests/setup.rs on_a_terminal_rerunning_setup_defaults_to_the_harness_already_configured: a config with default = "codex" still offered [claude]. tests/codex_sessions.rs assert_sessions_on_codex failed because a Codex prompt said "raising the Bash timeout".
  After: both pass, and the full cargo test and cargo clippy --all-targets pass.
• New suites: tests/harness_choice.rs (flags, fallback, checks before work, recording), tests/codex_sessions.rs (Codex sessions end to end), Setup's Harness scenarios in tests/setup.rs, plus additions to the Spec run, Pickup run, Architect run and Base fix suites.

Merge Danger

Door: two-way

The skill rename changes how every session loads its skills. Claude sessions no longer get --plugin-dir and instead find thirdshift-* skills in the worktree's .claude/skills/. The .git/info/exclude entries stay in each target repository.

Blast Radius: every-session

A user with no Harness settings keeps running on Claude Code with no extra calls. A repository with its own .claude/skills/ or .agents/skills/ gains thirdshift-* links beside its own skills. Codex sessions run unsandboxed, as ADR 0012 records.

Unaddressed findings

Standards

• Possible Data Clumps (Choice repeats ModelAndEffort's fields; --sessions-harness/-model/-effort are three loose options). Skipped: folding them is a wide refactor across the session seam for no change in behaviour. Better as its own clean-up.
• Possible Repeated Switches (match harness in harness.rs, session.rs, progress.rs, skills.rs, questions.rs). Skipped: with two Harnesses and Harness-specific choices, a per-Harness adapter trait is a larger redesign than this Spec needs.
• Possible Mysterious Name (harness.harness, the two claude_args/codex_args, Choice::test_call). Skipped: renaming across the seam is churn with no behaviour change, and the doc comments state each one's role.
• Possible Feature Envy (CLI arguments built partly on Choice, partly in session.rs). Skipped for the same reason as the Repeated Switches finding.
• Duplicated Harness::named in config.rs. Skipped: it's a match guard, which can't bind the Harness it finds.
• Duplicated filter in Catalog::model / Catalog::listed. Skipped: they're small and answer different questions.
• Stream::failed/error defaults that only Codex overrides. Skipped: the reviewer judged them acceptable.

Spec

• Setup skips the Harness question when neither CLI is installed, or when Codex's catalog can't be read. Skipped: saving a Harness that can't run, or an unchecked Model, would break "Setup never saves a value a Run would reject".
• - clears a Model or Effort in Setup, and blank keeps the current value (scope creep). Skipped: on re-run, blank keeping the current value is how every Setup question behaves (user story 28). Without -, there would be no way back to the Harness's default.
• The new thirdshift-resolving-merge-conflicts skill (scope creep). Skipped: the conflict-repair prompt already loaded that skill, which didn't exist, so the rename to thirdshift- names needed it.
• The longer thirdshift help section on the Harness (scope creep). Skipped: it documents the new flags, which users need.
• "Built with …" on a Run notification when the check failed. Skipped: the line names the Harness, Model and Effort the Command was given. A failed check reports the setting it rejected, which is what the reader needs.

Closes #136

Tickets

• Load the Factory skills from the worktree as thirdshift-<skill>, replacing the Claude plugin #391 landed with Load the Factory skills from the worktree as thirdshift-<skill>, replacing the Claude plugin #400
• Choose the Harness, Model and Effort on the command line and in the User config, with Claude #392 landed with Choose the Harness, Model and Effort on the command line and in the User config (#392) #402
• Setup asks for the Harness, Model and Effort #393 landed with Setup asks for the Harness, Model and Effort (#393) #403
• Run a Command's sessions on Codex #394 landed with Run a Command's sessions on Codex #404
• Resume and interrupt Codex sessions #395 landed with Resume and interrupt Codex sessions (#395) #405
• Setup offers Codex #396 landed with Setup offers Codex (#396) #406

🤖 Generated with Claude Code