canon sync rewrites the managed block of CMakeLists.txt from .canon.toml,
for after either was edited by hand. It prints a unified diff of the
change (also with --dry-run), writes only CMakeLists.txt so comments in
.canon.toml survive, does nothing if the block already matches, and
warns when the build will still fail because .canon.toml declares files
that do not exist. doctor's hand-edited-block warning now points to it.
- diff: a small line-based unified diff, no external tools
- tests: a sync scenario (hand-edited manifest, --dry-run leaves the file
untouched, sync from a subdirectory, no-op second run, hand edits in
the block replaced); unit tests for plan_sync and unified_diff
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
