toolsd-diff-patch-roundtrip-filename-mismatch

Answer

I diagnosed the problem live against the installed toolsd build and wrote the verified solution.

Deliverables

• ~/toolsd-diff-patch-roundtrip-filename-mismatch.md — full solution (root cause, exact fix, verification)
• ~/toolsd-roundtrip.sh — reusable, self-verifying round-trip helper

Diagnosis in brief

toolsd patch applies every file section to the +++ (new-side) path and requires that file to currently contain the --- (old-side) bytes. It is strict with zero fuzz (offset window of 0). When you diff a modified file against a differently-named unmodified copy, the +++ target already holds the final content, so the refusal is the no-silent-corruption contract working as designed — not a bug.

Reproduced exactly:

$ toolsd diff f.txt g.txt > p.diff   # --- f.txt / +++ g.txt
$ toolsd patch p.diff
toolsd: patch: hunk 0: does not apply: no exact match ... offset window of 0
toolsd: patch: rolled back - no files in the tree were modified   # exit 1

The fix (usage, not code)

Generate the patch while the +++-named file holds the new content, then reset that file to the old content before applying — piping via stdin so targets resolve against the CWD:

cp f.txt f.txt.orig          # snapshot before edit
$EDITOR f.txt                # f.txt = new content (the +++ side)
toolsd diff f.txt.orig f.txt > change.diff
cp f.txt.orig f.txt          # put the +++ target back at the old state
toolsd patch - < change.diff # patched 1 file(s) atomically

Also documented the secondary trap: toolsd patch FILE resolves targets against the diff file's directory, while toolsd patch - resolves against the CWD.

Verification

All captured live: byte-exact round trip via the helper, the context repro, no-newline-at-EOF round trip, empty-diff vs empty-patch distinction, and a troubleshooting table. The helper creates a sandbox, applies the patch to a copy of the old content at the +++ path, and asserts cmp equality before reporting success.