fix(toolpath-convo): consult git HEAD for Write-tool before-state

[eliothedeman]

Summary

• toolpath_convo::file_write_diff gains a before_state: Option<&str> parameter. For the Write { content } shape, Some(prior) becomes the diff pre-image; None preserves the old behaviour (diff against ""). Edit/MultiEdit paths are unchanged — they already carry their own old_string/new_string.
• toolpath-claude's Claude-JSONL deriver wires a best-effort git-HEAD lookup for Write invocations: shells out to git show HEAD:<relpath> using the turn's cwd (falls back to the conversation's project path). Silently returns None when the project isn't a git repo, the file isn't tracked at HEAD, or git isn't on PATH — the deriver then produces the existing additions-only diff.
• toolpath-convo bumped to 0.7.0 (public API break).

Closes #35

Test plan

• Unit: file_write_diff with Some(before) shows - lines for replaced content
• Unit: file_write_diff with None is addition-only (existing behaviour preserved)
• Unit: before_state ignored for Edit shape
• Unit: resolve_local_dir precedence (entry cwd > config > conversation), file:// prefix stripping
• Integration: real tempdir git init + commit + Claude Write tool → derived raw diff has -old-content and +new-content
• Integration: no-git tempdir + Claude Write → additions-only fallback (no - lines)
• cargo test --workspace (1209 passed, 0 failed)
• cargo clippy --workspace -- -D warnings clean
• All 12 example documents still validate

[github-actions]

🔍 Preview deployed: https://df5cbd6d.toolpath.pages.dev

[eliothedeman]

Summary

Cleanly fixes #35 by threading before_state: Option<&str> through file_write_diff / file_write_change and wiring a best-effort git show HEAD:<rel> lookup at the Claude call site. Public API break on toolpath-convo is properly versioned (0.7.0) and all four required locations are updated.

Notes

• crates/toolpath-claude/src/derive.rs:22-44 — git_head_content uses Command::new("git").arg(...) with -C, so no shell and no injection surface. format!("HEAD:{rel_str}") is passed as a single argv element. Safe.
• crates/toolpath-claude/src/derive.rs:51-60 — resolve_local_dir precedence (entry cwd > config > convo) is the right call per-turn; file:// stripping is handled once at resolve time.
• crates/toolpath-claude/src/derive.rs:533-553 — only Writes consult git; Edit/MultiEdit correctly skip the lookup. .and_then chain means any failure (no repo / untracked / git missing) falls through to additions-only.
• crates/toolpath-convo/src/derive.rs:175-179 — shared deriver passes None with an explanatory comment about providers with local checkout access overriding. Clean boundary.
• Tests: both paths covered — unit tests for Some/None/Edit-ignored, plus two real tempfile + git init integration tests asserting -old-content / no removal lines. Matches the rubric.
• Versioning: crates/toolpath-convo/Cargo.toml, workspace Cargo.toml, site/_data/crates.json, CHANGELOG.md all updated to 0.7.0. Cargo.lock reflects it. CI green.
• No scope creep; no feature flags or backcompat shims.

Verdict

Approve (posted as comment — GitHub blocks self-approval). Surgical fix, correct API shape, safe subprocess call, symmetric tests, versioning complete.