fix(trg): split capability offered from capability driven

[yordis]

• The support matrix answered two different questions with one value: whether a harness offers a control, which is a fact read off that CLI's --help, and whether trg builds its invocation from it, which is a fact about our own code. Folding them together meant a cell could look authoritative and drive nothing, and five of the eight controls were in exactly that state.
• A reader who saw claude-code listed against --allowedTools would reasonably conclude that trg restricts tools during a run. It does not, and nothing in the type or the tests said otherwise.
• The existing table test guards the doc against the declaration, not the declaration against the invocation code. It would have passed unchanged if every runner ignored the matrix entirely, which was very nearly the case. The reference doc claimed more than that test delivers, so the doc is corrected too.
• The fix is in the type rather than in a new assertion: a mechanism is now reachable only through the driven state, so an argument builder cannot be constructed from a cell trg does not exercise. Promoting a cell obliges you to write the invocation that consumes it, which is a compile-time guarantee rather than something a test has to remember to check.
• Recording the other five as offered rather than deleting them keeps a fact worth having. mcp servers and conversation resume are the prerequisites for MCP mocking and conversation seeding, and this is precisely the state those items would move out of.

[cursor]

PR Summary

Low Risk
Refactor of capability metadata and tests/docs; runner argv behavior is unchanged except clearer typing that prevents mis-wiring offered controls.

Overview
Harness capability modeling now separates what a CLI exposes from what trg actually drives. ControlMechanism holds flag/subcommand/env/reported shapes; ControlSupport is Absent, Offered (documented as (harness only)), or Driven (used in invocation). flag() only reads Driven flags, so argument builders cannot pull mechanisms from cells trg does not wire.

The support matrix is reclassified: controls like tool allowlist, MCP, system-prompt append, and conversation resume are Offered where the harness has them but trg does not pass them; sandbox levels, run-scoped config home, and cost reporting stay Driven where trg uses them.

Tests and docs add every_driven_flag_is_carried_by_the_invocation_it_drives (via pub(crate) build_args on each runner), tighten config-home/pricing checks to Driven, and update the Harness support reference table and prose to match.

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• crates/trg/docs/reference/ai-skills-eval.md

Walkthrough

The runner capability model now separates offered controls from driven controls. Runner argument builders are crate-visible for validation. Tests cross-check driven flags against built invocations. The reference table marks harness-only controls.

Changes

Runner capability validation

Layer / File(s)	Summary
Support model and runner declarations crates/trg/src/agentskills/runner/capabilities.rs	Adds ControlMechanism and wraps support values as Absent, Offered, or Driven. Updates runner declarations, formatting, and related assertions.
Invocation access and validation crates/trg/src/agentskills/runner/{claude_code,codex,cursor_agent}.rs, crates/trg/src/agentskills/runner/capabilities.rs	Makes each runner’s build_args available within the crate. Tests verify that every driven flag appears in the built invocation.
Support reference documentation crates/trg/docs/reference/ai-skills-eval.md	Marks controls that Harness offers but trg does not exercise as (harness only). Documents the declaration and invocation checks.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🔵 Low · up to 40ae4

The reference documentation overstates validation for environment and reporting controls. Clarify the claim or extend the checks before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 61.54% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 4 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: separating offered capabilities from capabilities driven by trg.
Description check	✅ Passed	The description directly explains the capability distinction, type changes, compile-time guarantee, documentation updates, and retained offered capabilities.
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 61.54% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 13 functions across 4 files. (1 skipped: 1 unsupported.)

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_{A rabbit checks each runner’s track
Offered signs stay on the stack
Driven flags appear in flight
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The support table now shines bright}

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Actionable comments posted: 1

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Inline comments:
In `@crates/trg/docs/reference/ai-skills-eval.md`:
- Around line 1046-1048: Update the documentation claim near
`every_driven_flag_is_carried_by_the_invocation_it_drives` to say invocation
validation covers driven `ControlMechanism::Flag` values only. Do not imply that
config-home or pricing checks validate the built environment or reported cost
fields; preserve their narrower declaration comparisons.

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between dd3d8d3 and 40ae443.

📒 Files selected for processing (5)

• crates/trg/docs/reference/ai-skills-eval.md
• crates/trg/src/agentskills/runner/capabilities.rs
• crates/trg/src/agentskills/runner/claude_code.rs
• crates/trg/src/agentskills/runner/codex.rs
• crates/trg/src/agentskills/runner/cursor_agent.rs

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