🤖 feat: include model + thinking in bash tool env

[ThomasK33]

Expose model + thinking level for PR attribution via bash env vars.

• getMuxEnv(...) now supports optional { modelString, thinkingLevel }
• AIService threads the current model + effective thinking level into tool env as:
  • MUX_MODEL_STRING
  • MUX_THINKING_LEVEL
• docs/AGENTS.md updated to require the new attribution footer format.

Validation:

• bun test src/node/runtime/initHook.test.ts
• make static-check

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📋 Implementation Plan

Plan: Extend GitHub PR attribution with model + thinking level

Problem

Today, PR bodies often end with a simple attribution footer like:

• _Generated with \mux`_`

You want that attribution to also include:

1. The model used to generate the changes.
2. The thinking level used.

Goals

• Provide a standard, copy/pasteable attribution footer format that includes model + thinking level.
• Make the exact model + thinking level available to the agent at runtime so the footer can be accurate (no guessing).
• Keep changes minimal; avoid introducing a full GitHub integration feature unless required.

Non-goals (for this iteration)

• Automatically creating PRs from inside mux via a dedicated “Create PR” tool/UI.
• Retroactively editing existing PRs server-side via GitHub Actions.

Recommended output format

Make the footer a single line (easy to scan) plus optional machine-readable comment (easy to parse later):

---
_Generated with `mux` • Model: `<modelString>` • Thinking: `<thinkingLevel>`_
<!-- mux-attribution: model=<modelString> thinking=<thinkingLevel> -->

Notes:

• Use the full mux modelString (e.g. openai:gpt-5.2-pro) to avoid ambiguity.
• thinkingLevel should be mux’s unified values: off|low|medium|high|xhigh.
• No PR URL/number is included in the PR body attribution (it’s already on the PR).

Approach options

Approach A (recommended): Expose model/thinking context + update instructions (low risk)

Net LoC estimate (product code only): ~40–90 LoC

Implement:

• Surface modelString + thinkingLevel in the bash tool environment as MUX_MODEL_STRING and MUX_THINKING_LEVEL so gh pr ... workflows can reference them.
• Update repo AGENTS.md guidance to require the richer attribution footer.
• Do not inject thinkingLevel into the system prompt (to avoid prompt-cache misses when switching e.g. high → medium).

Why this is enough:

• mux doesn’t currently own PR creation; agents typically run gh via the bash tool.
• Env vars are available exactly where PR bodies are usually authored (shell workflows) without changing the LLM prompt/caching behavior.

Approach B: Add a helper CLI/script for “create PR with mux attribution”

Net LoC estimate (product code only): ~0 LoC (mostly script/docs), or ~200–400 LoC if built into mux CLI/tools.

Implement a script (e.g. scripts/gh_pr_create_with_mux_attribution.ts) that:

1. Creates the PR via gh pr create ....
2. Ensures the PR body includes the attribution footer using $MUX_MODEL_STRING / $MUX_THINKING_LEVEL.

This makes “add the correct footer” a single command, but is more opinionated and adds surface area.

Detailed implementation plan (Approach A)

1) Preserve prompt caching behavior

• Do not add per-request dynamic metadata (especially thinkingLevel) into the system prompt.
  • Prompt caching (e.g. Anthropic prompt caching) keys off the input; changing the system prompt when switching high → medium would reduce cache hits.
• Therefore, this change intentionally avoids modifying buildSystemMessage(...).

2) Add env vars for bash-based PR flows

• Extend getMuxEnv(...) to optionally accept { modelString, thinkingLevel }.
• Populate:
  • MUX_MODEL_STRING=<modelString>
  • MUX_THINKING_LEVEL=<thinkingLevel||off>

Files:

• src/node/runtime/initHook.ts (extend getMuxEnv signature + implementation)
• src/node/services/aiService.ts (pass model/thinking into getMuxEnv for tool calls)

Notes:

• Keep existing callers intact by making the new argument optional.
• It’s OK that init hooks (which aren’t tied to a model invocation) won’t always set these vars.

3) Update AGENTS.md guidance to require the richer footer

• Replace the existing instruction about _Generated with \mux`_` with the new required template.
• Add a short note:
  • model/thinking values should be sourced from $MUX_MODEL_STRING and $MUX_THINKING_LEVEL in bash (preferred; doesn’t affect prompt caching).

Files:

• AGENTS.md
• docs/AGENTS.md (keep in sync if both are published)

4) Tests

Add/update unit tests so this doesn’t regress:

• Add/extend a getMuxEnv unit test (either new or in an existing runtime test file)
  • getMuxEnv includes the new env vars when options are provided.
  • Existing env vars remain unchanged.

Validation steps (manual)

• In a bash tool call (or any gh workflow), run:
  • echo "$MUX_MODEL_STRING"
  • echo "$MUX_THINKING_LEVEL"
• Create/update a PR body footer and confirm it renders as expected.
• Switch thinking level (e.g. high → medium) and confirm prompt caching behavior is unchanged (since the system prompt isn’t modified by this feature).

Decisions (confirmed)

• Footer includes only model + thinking level (no PR URL/number).
• Footer label uses Thinking: (aligns with mux naming) and records the mux thinkingLevel value (off|low|medium|high|xhigh).
• Include the hidden HTML comment for machine parsing.
• Use the current modelString/thinkingLevel at PR creation/update time (no aggregation across sessions).

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Generated with mux • Model: openai:gpt-5.2 • Thinking: high