docs: explicit model param on Agent calls + Sonnet default for PR-shipping

[cristim]

Summary

Adds two bullets to CLAUDE.md §"Subagent Strategy" tightening the existing "delegate to the cheapest sufficient tier" rule:

1. Always pass model explicitly on every Agent call — never rely on inheritance. Omission silently makes Opus the de facto tier for every subagent of an Opus session — a 5–10× cost premium for work that almost always doesn't need it. If you genuinely want the parent's tier, still pass it explicitly so the choice is visible at the call site.

2. Routine PR-shipping defaults to Sonnet end-to-end. The standard pattern (plan + 3-pass review + worktree + implement + test + push + open-PR + ping-CR + arm-CI-watcher) is Sonnet-tier work even including the plan and review iterations. Empirically clean when the issue's acceptance criteria are clearly enumerated. Escalate to Opus per-fork only when a specific signal during review surfaces real design judgment (shape not pre-decided, competing approaches need weighing, subtle invariant surfaced that no acceptance criterion captured).

Test plan

• Read CLAUDE.md §"Subagent Strategy" lines 213–217 — the two new bullets sit alongside the "Default: delegate down" rule and the existing rubric, and the three together read as one coherent escalation policy
• Confirm "explicit model" rule doesn't contradict the "main session's tier set by user" line (line 222) — they're compatible: line 222 governs the main thread, the new rule governs Agent spawns
• `git diff --stat origin/main` shows exactly one file changed (`CLAUDE.md`), 2 insertions, 0 deletions

Summary by CodeRabbit

• Chores
  • Updated internal development guidance and workflow documentation.

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Note: This release contains no user-facing changes.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 060ba204-4004-457d-9e1e-9177e7c828d6

📥 Commits

Reviewing files that changed from the base of the PR and between 670ee2f and 9bc19dd.

📒 Files selected for processing (1)

• CLAUDE.md

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📝 Walkthrough

Walkthrough

Updated documentation in CLAUDE.md to establish two default guidance rules: always explicitly pass the model parameter on every Agent call to prevent unintended inheritance, and default routine PR shipping to Sonnet tier unless an explicit escalation reason exists.

Changes

Agent Modeling Guidance

Layer / File(s)	Summary
Documentation Update CLAUDE.md	Added guidance requiring explicit model parameter on every Agent call and establishing Sonnet as the default model tier for routine PR-shipping workflows unless escalation is justified.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related issues

• docs(claude): codify model-selection + PR-labeling rules surfaced in cross-repo work #8: Addresses identical guidance requirements for explicitly passing model on Agent calls and defaulting routine PR-shipping to Sonnet end-to-end.

Possibly related PRs

• docs(claude): codify model-selection + PR-labeling rules (closes #8) #9: Modifies CLAUDE.md with the same agent-modeling rules regarding explicit model parameters and Sonnet defaults for routine PR-shipping.
• feat(gemini): add gemini model mapping and always-on triage rules #7: Overlaps on the requirement to always pass an explicit model parameter when spawning subagents/Agent instances.
• docs: downshift model recommendations toward cheaper tiers #1: Related through model-tiering and default-model guidance updates to CLAUDE.md, though may contain conflicting decisions on model selection.

Suggested labels

triaged, type/docs, effort/xs, impact/internal, severity/low, urgency/eventually, priority/p3

Poem

🐰 A model must be named, not guessed with care,
Let Sonnet lead the shipping everywhere!
No silent inheritance—pass it true,
Two lines of wisdom, crystal-clear and new. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and concisely summarizes the two main changes: adding an explicit model parameter requirement and setting Sonnet as the default for PR-shipping workflows.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/explicit-model-rules

⚔️ Resolve merge conflicts

• Resolve merge conflict in branch docs/explicit-model-rules

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[cristim]

Superseded by commit b3f64d6 ("docs(claude): codify model-selection + PR-labeling rules", closes #8) — main already contains the explicit-model-param and Sonnet-default-for-PR-shipping bullets verbatim. Closing rather than rebasing into a no-op merge.