#19780 Agent pane: Show more lines in the changes view (cx-ncc.85, 3/3)

Part of cx-ncc.85 (Claude parity): Show more lines in the changes view. This is step 3 of 3, the page side. Steps 1 and 2 are #19732 (session host context_lines, landed) and #19730 (App pass-through).

In a git scope (Uncommitted, Unstaged, Staged, Committed, Branch), each changed file is read a second time as it scrolls into view. The second read is git.diff with paths: [file] and context_lines: 1_000_000, so it holds every unchanged line. From that read the page rebuilds both versions of the file and hands Pierre the scope's own patch with them (processFile(patch, {oldFile, newFile})). The diff is then no longer partial, and Pierre's hunk separators get their expand buttons: up, down, or both between hunks.

• What stays the same. The shown hunks are still the scope's, so staging, hunk keys, review threads and find don't change.
• When the read is not used:
  • its changes differ from the shown diff (the file changed since the scope loaded);
  • the patch was cut short;
  • the answer has more than one hunk, as from an App without #19730, which ignores the new params. The diff then stays exactly as it is today.
• Skipped files: renames (a one-path read would lose the old name), created, deleted and binary files, truncated patches, and Last turn.
• Request count: one read per file per scope load, cached, and only for files that come within 400px of the viewport.
• Mock: the mock daemon answers paths and context_lines from its fixture contents.

Verification

Behavior test: webviews/test/changes-more-lines.test.tsx renders DiffPanel in JSDOM with Pierre and checks:

• Unstaged reads a.txt whole;
• the diff gets expand buttons;
• a hidden line between two hunks shows after the separator is clicked;
• a stale whole read is not used;
• without a whole-file source the diff is unchanged.

Results:

• Red at f671e3898441 (test only): 2 pass, 1 fail. The view never read the file ([] instead of [["unstaged","a.txt"]]).
• Green at 6f6fd794f22a: 3 pass, 0 fail. changes-stage and changes-pull-request still pass, 12 in all.
• bun run check, bunx tsc --noEmit -p ., gallery-coverage and ui-rules all pass.
• Review fix (review subagent):
  • Red at 67ead56cbf1d, 3 pass and 1 fail. A host that ignores or caps context_lines returns a read starting at line 20, and that read was used, so the rebuilt file was too short.
  • Green at 6b1285979276, 4 pass and 0 fail. A read must start at line 1 on both sides.
• Known gaps (Low in review, not fixed here):
  • After a stage or reload, visible files re-read and flip from partial to whole.
  • Files over the host's 256 KB patch cap come back truncated and never expand, but the host still runs the read.
  • A capped read that starts at line 1 but stops before the file's end shows that point as the file's end.
• Gallery: agent-pane.diff-panel more-lines. Its play expands the separator between the two hunks and waits for the hidden lines.
• No new user-facing strings.

Changelog

Added: the changes view's git scopes can show the unchanged lines between and around a file's hunks.

🤖 Generated with Claude Code

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Summary by cubic

Makes the changes view's git scopes show the unchanged lines between and around hunks, matching the Claude behavior. Each changed file is re-read with git.diff using paths and context_lines: 1_000_000 as it scrolls into view; the full read lets Pierre's hunk separators expand. The shown hunks, staging, hunk keys, review threads, and find stay unchanged — only the surrounding context is added.

Notes

• The whole-file read is skipped for renames, created, deleted, and binary files, truncated patches, and the Last turn scope; one read per file per scope load, cached.
• A read that doesn't start at the file's first line is discarded, as it comes from a host that ignored or capped context_lines and rebuilding from it would shorten the file.
• Requires the session host to accept paths and context_lines (landed in #19732) and the App to pass them through (landed in #19730).

Showcase

Open the live gallery