feat: add native mergiraf tool

[trotsky1997]

Summary

• add native mergiraf tool contract for merge, solve, and languages actions
• execute mergiraf via argv-safe local process spawning with bounded JSON envelopes
• register mergiraf in the built-in catalog and allow-list behavior
• add fake-binary tests for catalog, argv construction, result envelopes, missing-binary guidance, and truncation

Validation

• cargo fmt
• cargo test mergiraf
• cargo test --test mergiraf_tool
• cargo test
• openspec validate mergiraf-native-support --strict --json

Refs #36

Remaining OpenSpec tasks in this change: documentation tasks 3.1-3.3 (README, spec/tools.md, ra.toml/init template docs).

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[trotsky1997]

Review request note: I attempted to add GitHub reviewer other-top-model, but GitHub returned Could not resolve user with login 'other-top-model'. No addressable GitHub reviewer/team by that name is available from this checkout; review handoff remains to the Multica/owner workflow.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Pass --git so merge updates the ours file

For real mergiraf merge calls this argv omits the merge-driver flag, so the command only prints the merge result to stdout and leaves the ours path unchanged. I checked the upstream CLI semantics: the documented Git driver form is mergiraf merge --git %O %A %B, and the implementation writes back to the left/ours file only in the git branch; otherwise it prints the result. In any workflow expecting this native tool to resolve the working-tree file in place, the tool can return ok: true while the conflicted file remains unmodified.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Enforce max_output_bytes for oversized envelopes

When max_output_bytes is smaller than the fixed JSON envelope, or when stderr/command metadata alone exceed the budget, this branch returns the rendered JSON even though it is still over the requested limit. For example, max_output_bytes: 1 or a very long stderr/cwd still produces an over-budget response despite truncated: true, which violates the tool contract that callers can bound returned output size.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Pass the language override through solve

When solve is used on a conflict file whose extension does not identify the language, upstream mergiraf needs the same --language/-L override that it supports for merge; I checked the upstream CLI, where the shared MergeOrSolveArgs is flattened into both Merge and Solve, and upstream tests run mergiraf solve --language=json. This wrapper accepts language but ignores it for solve, so a caller-supplied override still results in a failed solve for otherwise resolvable files.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Don't emit unsupported --allow-parse-errors

When allow_parse_errors is true, the wrapper appends a flag that the current mergiraf CLI does not define; I checked the upstream merge/shared option definitions and they include --debug, --compact, marker length, --language, merge-specific flags like --git, but no --allow-parse-errors. With a real binary this makes the documented option fail argument parsing before any merge runs.

Useful? React with 👍 / 👎.