🤖 feat: allow model and thinking overrides on sub-agent launch

[ammar-agent]

Summary

Adds optional model and thinking parameters to the task (sub-agent launch) tool so a launching agent can override the spawned sub-agent's model and thinking level. Both default to the existing inherit semantics, and the param descriptions instruct the model to omit them unless explicitly told otherwise (and to never assume a particular model is available).

Background

Previously a sub-agent's model/thinking were always inherited (parent live runtime env → parent workspace AI settings → per-agent config defaults → global default). There was no way for a launching agent to request a specific model/thinking for a delegated task. The override slots (TaskCreateArgs.modelString / thinkingLevel) already existed at the top of resolveTaskAISettings' precedence chain but were never wired to the tool.

Implementation

• Schema (toolDefinitions.ts): new model and thinking fields on the task tool, both .nullish() (strict-mode convention). thinking is preprocessed to coerce a JSON number to a string before parsing.
• Handler (tools/task.ts): parseTaskAiOverrides parses the inputs reusing the exact UI logic and forwards them to taskService.create. Invalid input throws a descriptive tool error before any task is spawned. The parent runtime fallback hint is still forwarded so unspecified fields keep inheriting.
• DRY model parsing: relocated normalizeModelInput from src/browser/utils/models/ to src/common/utils/ai/ (history preserved via git mv; its only deps were already in common), updated the browser importers, and collapsed the duplicate ACP normalizeModelForCommand onto the shared helper.
• DRY thinking parsing: handler uses parseThinkingInput (named levels OR numeric indices). Numeric indices stay deferred as ParsedThinkingInput and are resolved against the chosen model's policy via resolveThinkingInput inside resolveTaskAISettings (so 2 means the same thing it does for /model+level in the UI). TaskCreateArgs.thinkingLevel was widened from ThinkingLevel to ParsedThinkingInput; existing concrete-level callers are unaffected (named levels pass through unchanged).

Validation

• make static-check green (lint, typecheck, docs sync regenerated for the two new tool params).
• New tests: task-tool handler forwards an alias + named thinking, forwards a numeric thinking as a deferred index, and rejects an invalid model before spawning; taskService resolves a numeric thinking override against the inherited model's policy. Full taskService.test.ts (150) and task.test.ts (23) pass.

Risks

Low. Behavior is opt-in; omitting both params preserves the prior inherit path exactly. The thinkingLevel type widening is backward-compatible (named levels are a subset of ParsedThinkingInput and pass through resolveThinkingInput unchanged). The ACP refactor is a straight delegation to an already-tested helper.

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Generated with mux • Model: anthropic:claude-opus-4-8 • Thinking: xhigh

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[ammar-agent]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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