diff: the pane reads every file's hunks with one git process, where it started one per file - #98445

Summary

TLDR: the diff pane starts one git process to read a change's hunks, where it started one per file

Up to fifty processes after every tool call become one. It matters most where starting a process is slow, as on Windows: one process can fail or run out of time where up to fifty could.

Notes

• One git diff --raw -z -p over the drawn files' literal paths prints their names, NUL-ended and unquoted, then every patch. The n-th patch is the n-th name's; no name is read out of a line, so a space, a quote, a newline, letters outside ASCII or b/ in a name cannot move a body.
• Each file's text goes through the same parse as before: the 400-line cut, "Large file" past 1 MB, binary, renamed, untracked and staged-then-edited rows read as they did.
• A failed read now blanks all the hunks ("Diff unavailable" on every file) where it blanked only the failed file's; the list and totals stay. One process can fail or run out of time where up to fifty could.
• The output limit (4 MiB) and the 5 s limit are one process's. Past the output limit, files that arrived whole keep their hunks and the rest are read by a second process; so are paths too long for one command line (12,000 characters a process).
• Seen on git 2.43, 2.50 and 2.53, not stated by git's manual: an empty field parts names from patches, and both come in one order. An opening line that git did not quote must equal the one its name gives, or the read fails; never a body under another name.
• A conflicted file is read like any other, and the files beside it keep their hunks. Against the index, where git prints no patch for an unmerged path, that path reads "No diff content", as before.
• Two differences. A file replaced by a folder of its name showed the folder's files' lines in its own body; it shows its own. In a file turned link, the line naming the new side reads +++ b/<name> whatever prefix a person's git config sets.
• Forced colour, an external diff, a textconv filter, a pager, core.quotePath and diff.renames change nothing: every pin of the old call is kept.
• The diff also tidies what it touches: a doc comment and two lines of the register module, one test title, one fixture comment. No other behaviour changes.

Test Plan

• claude plugin test mods/diff passes
• Change 50 files, open /diff, watch the process list through a tool call: one git diff reads the hunks
• Change files named with space.txt, quo"te.txt and x b/x.txt: each shows its own hunks
• Change one file by 5 MB and two small ones after it: the first says "Large file", the others show hunks

Revert-proof: 36 new tests fail with the modules' changes reverted (the mod's own suite, run against the unchanged modules)

Changelog