fix: render valid TOML when a command body contains backslashes

[jawwad-ali]

Description

CommandRegistrar.render_toml_command() renders a command body into a multiline basic TOML string ("""..."""). Basic strings process backslash escape sequences, but the body was emitted raw — so any backslash in the body breaks the output:

• A Windows path like C:\Users\... contains \U, which TOML reads as an 8-digit unicode escape → the agent's TOML loader fails with Invalid hex value and the generated Gemini / Tabnine command file is completely unparseable.
• A body ending in a single \ becomes a TOML line-continuation that silently swallows the closing newline.

Reproduced with tomllib:

render_toml_command({}, r"Run C:\Users\dev\tool.exe", "src")
# -> prompt = """ ... C:\Users\dev\tool.exe ... """
# tomllib.loads(...) -> TOMLDecodeError: Invalid hex value

Fix

Route bodies containing a backslash away from the basic-string branch: prefer the multiline literal form ('''...'''), which does not process escapes, and fall back to the escaped basic string (_render_basic_toml_string) when both triple-quote styles are present. This mirrors the backslash escaping already done by base.py's TomlIntegration. One-line condition change; behavior is unchanged for backslash-free bodies.

Testing

• Tested locally with uv run specify --help (exit 0)

• Ran existing tests with uv sync && uv run pytest

• uvx ruff check src/ — All checks passed

• uv run pytest tests/test_extensions.py tests/integrations/test_integration_gemini.py tests/integrations/test_integration_tabnine.py — 381 passed, 3 skipped (no regressions; the existing 3 render_toml_command tests still pass).

• New tests in tests/test_extensions.py: a Windows-path body, a trailing-backslash body, and a backslash + both-triple-quote-styles fallback — each asserts tomllib.loads() succeeds and the body round-trips. The first two fail on main (TOMLDecodeError / dropped backslash) and pass with this fix.

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Found and fixed with Claude Code (Claude Opus 4.8) under my direction. AI located the unescaped basic-string branch, confirmed the existing TomlIntegration escaping precedent, implemented the routing fix, and wrote the tests; I reproduced the tomllib parse failure on main and verified the fix + no regressions in the Gemini/Tabnine suites before submitting. I'll disclose if any review responses are AI-assisted as well.