diff

The diff pane as a plugin: /diff opens the session's uncommitted changes beside the transcript, one row per changed file and every file's hunks beneath, a row's click scrolling to its file, and closes it again; each toggle leaves Diff panel shown or Diff panel hidden in the transcript. The pane refreshes as Claude edits, runs shell commands and finishes turns, and while it is open it polls the repository's HEAD so a commit or checkout made elsewhere shows too. The first successful edit of a session opens the pane by itself where the terminal is wide enough (144 columns when the person never chose, 110 when they kept it open before; a person who closed it is left alone). On a terminal under 110 columns /diff answers with the built-in's line asking for a wider terminal and opens nothing; a pane the surface seats inline on a terminal that wide shows only that line, and on a wider one (a session without the fullscreen layout) the built-in dialog's layout: the rows round the selected file and that file's hunks. A file's ask button arms that file: its hunks ride the next prompt as context, once.

The pane compares the working tree against HEAD, split at the session's start (the default), against HEAD plainly, or against the merge-base with the default branch; the choice is kept per repository in the plugin's store. A second picker shows one earlier turn's edits instead of the working tree, read from the session's messages. Files that changed before the session started (by their timestamp, among the paths already dirty at the start), and noise (lockfiles, generated and test files), are listed apart and folded until asked for; a rename lists as git prints it. Outside a git repository /diff says so and does nothing else.

hooks/register.ts is the module; everything under hooks/ is its parts.

What it hooks

event	what the hook does
session.start	Binds the engine once, registers /diff (a session where another /diff is listed leaves the plugin idle), and pins the repository.
ui.render of PromptHint	Reads the terminal's width, which decides whether the first edit opens the pane.
ui.render of Pane	Draws the pane: header, the base and source pickers, the file list, the toggles, and the files' hunks.
command.run of diff	Opens or closes the pane, says which, and remembers the choice.
ui.close of the pane	Remembers the person's close as /diff's.
command.run of clear, resume	Closes the pane and forgets the session's state.
tool.call of Edit, Write, NotebookEdit	After the edit, refreshes an open pane; the session's first successful edit opens it.
tool.call of Bash, PowerShell	After the command, refreshes an open pane.
turn.complete	Refreshes an open pane.
prompt.submit	Adds the armed file's hunks to the prompt's context and disarms.

What it calls on $

clock.after, clock.every, clock.now, command.register, fs.list, fs.read, fs.stat, process.run (git, read-only), session.messages, store.get, store.set, telemetry.log, telemetry.mark, ui.close, ui.invalidate, ui.log, ui.open, ui.resolve, ui.scroll, ui.status.

$.telemetry is the telemetry plugin's noun; where it is absent the rows are dropped and nothing else changes.

Try it

claude --plugin-dir /path/to/diff

then /diff inside a git repository with a modified file.