[stippi]

Closes the remaining gaps between the pull request view (#292) and T3 Code's, except the Guide tab. Each part follows T3's behaviour and texts; docs/pull-request-view.md describes all of it.

Code tab

• Stacked | split (remembered): split rows pair a hunk's removed and added runs, old numbers left, new right; new and deleted files stay one column; threads and comments go below the row showing their line.
• Hide whitespace changes (on by default, like T3): GitHub's API has no whitespace-free diff, so like T3 each hunk is diffed again without whitespace, per page off the UI thread.
• Wrap (remembered): unwrapped rows scroll sideways together per file; the line numbers stay put.
• Expand context: gaps between hunks and the unknown tail get T3's buttons (100 lines up or down, or all; shift-click for all). The first click reads the file through pull_request_file_contents, one read per file at a time, and highlights both whole sides.
• File tree (right side, remembered): folders with a single child folder are drawn as one row; files are tinted by their change with its letter. A click unfolds the file and scrolls to it.
• On narrow toolbars, the whitespace, wrap and layout options fold into a menu.
• DiffRows now draws one or two cells per row and selects by flat line, which a split chunk needs.

Check out

• Works like gh pr checkout (git::pull_request):
  • The head comes from the PR repository's remote.
  • A fork's head is fetched as refs/pull/N/head, without adding a remote. It tracks the fork's branch when maintainers may push, otherwise the PR ref.
  • A fork branch named like the default (or base) branch becomes owner/branch.
  • An existing branch only fast-forwards.
• In a separate worktree reuses the branch's worktree or creates one beside the project. A new session for the project works in it, knows the PR as its own, and opens with the PR beside it.
• In this repository refuses to switch when there are tracked changes (as T3 does); the session follows its new branch.

Stacked pull requests

• github reads stacks via repos/o/n/stacks?pull_request=N, revalidated with ETags; 404 means no stack.
• On github.com, listings mark which rows sit in a stack.
• Merging a stack uses merge-async and polls until GitHub settles.
• A rebase first checks the stack is unchanged and every branch is writable. git::stack_rebase then replays the layers in a scratch repository and pushes with a lease. The credential only goes through GIT_CONFIG_*.
• In the UI:
  • The header gets T3's stack menu (layers, base, Merge stack / Rebase stack) and a "Merge stack" button. Both ask for confirmation over the panel.
  • While a PR is in a stack, or its stack isn't known yet, the single-PR merge controls are hidden.
  • List rows get the "⧉ 2/3" popover, which reads the stack only once opened.

Workflow approvals

• For an open fork PR, the detail read lists the runs waiting for approval and shows them as checks. The checks poll also revalidates the fork's runs.
• "Approve workflows to run" takes the checks' place on the Summary tab (two clicks). Before approving it re-reads the head, and it refuses a head that another open PR shares.
• The checks popover now orders checks the way T3 does: attention first, then running, then completed behind "Show all", each with a "Details" link.

Tabs

• Each opened PR gets its own tab next to the list tab. You can:
  • close a tab with the button, a middle click, or the context menu (others / to the right / all);
  • reorder tabs by drag and drop;
  • scroll the tab row with arrows when it overflows.
• Each tab keeps its page (scroll position, sub-tab, drafts). Only the visible tab reads data and polls.
• Open tabs are remembered per session. The back arrow is gone, since the list is one tab away.

Verification

• cargo fmt --check, cargo clippy --all-targets --all-features -D warnings and cargo deny check are clean, and the workspace tests pass. Three code_assistant_core tests (browser and recovery timing) failed only under a full parallel run and pass when run alone.
• Tried in the running app against stippi/code-assistant, with an isolated config and data copy and a scratch clone as the project:
  • split, file tree, wrap with sideways scrolling, expanding context;
  • tabs, including restore after a restart;
  • the checks popover;
  • checking out fork PR chore: add luna models to catalog #291 into a new worktree session (fork URL upstream, as gh does);
  • checking out Custom file renderers configured in the settings #286 "here".
• Not tried live:
  • Stack merge/rebase: no stacks exist in these repositories. Covered by tests with the fake transport and a local git remote.
  • Clicking "Approve workflows": no runs were waiting, and I didn't approve anything on GitHub.