[AR307]

Summary

Keep the work panel's preferred width when a manual sidebar reopen squeezes the
panel. The reopen stored the squeezed width as the user's width, so the panel
stayed narrow after the sidebar collapsed again or the window grew, and the
narrow width survived a restart. When the squeezed width was below 244px, the
divider minimum also dropped to 1px.

• A sidebar reopen now lends width to the sidebar instead of storing it. The
  loan lives only in renderer memory. Extra client width goes back to the panel
  first, and collapsing the sidebar or resizing the panel ends the loan.
• Resize gestures keep the 244px minimum. A panel shown narrower than that
  starts a drag from its current width and cannot be dragged narrower.
• Stored widths below 244px, which only the old reopen path could write, load
  as 244px.

The reopen priority of ADR 0238 is unchanged: the panel gives up width first
and MainChat lands on its 460px target. Decision 3 of that ADR, which allowed
the compact width to be persisted, is amended.

Reproduction

Reproduced against main 4f9f051e54c495ac0c5164f2ef4dd687c704bc11 on
October 17, 2026, in an 866px shell with the default 275px sidebar and a
360px panel.

Reopen the sidebar, then collapse it again

1. Open a conversation and its work panel at 360px. The 360px panel does not
   fit beside the sidebar, so the layout collapses the sidebar.
2. Reopen the sidebar. The panel shrinks to 131px so MainChat keeps 460px.
3. Collapse the sidebar again.

Before: The panel stays at 131px although 416px are available.
pi.desktop.workPanel now holds {"width":131}, so the next launch also
opens the panel at 131px.

After: The reopen shows 131px without storing it. Collapsing the sidebar
restores 360px, and the stored width stays {"width":360}.

Drag the divider after the reopen

1. After the steps above, drag the work-panel divider to make the panel
   narrower.

Before: The stored width is below 244px, so the gesture uses the 1px
compact minimum and the panel can be dragged down to a 1px sliver. Dragging it
back above 244px restores the limit, so the minimum appears and disappears.

After: The drag stops at 244px.

Any constrained reopen overwrote the preferred width. With the 800 DIP window
minimum and default widths, the squeezed width falls below 244px at shell
widths up to about 978px, or in wider windows with a wider sidebar.

Changes

• work-panel-resize.ts:
  • workPanelRequestedWidth resolves the width the panel asks of the
    three-column budget: the preferred width, or the lent width while the
    reopened sidebar stays expanded, with extra client width given back to the
    panel first.
  • workPanelGestureMinimum gives resize gestures the 244px minimum, or the
    shown width when that is narrower.
• Work-panel slice:
  • workPanelYieldedWidth is runtime-only state, set through
    setWorkPanelYieldedWidth.
  • setWorkPanelWidth keeps the 244px minimum and ends a loan.
  • loadWorkPanelWidth raises stored widths below 244px.
• useAppShellRuntime:
  • The reopen sets the lent width instead of calling setWorkPanelWidth.
  • The loan ends once the sidebar has fully collapsed, whichever path
    collapsed it.
  • The sidebar resize budget and the pending dock in AppShell use the
    requested width, so the sidebar resize range follows the shown panel width.
• WorkPanel:
  • The layout uses the requested width, except during a drag preview.
  • The gesture minimum follows the shown width.
  • A resize key that cannot move the separator commits nothing.
• Docs:
  • ADR 0238 decision 3 is amended.
  • 01-ui-ia, 09-interaction-patterns and
    E2E-LAYOUT-three-column-width-priority are updated, with their zh-CN
    mirrors.
• Tests:
  • Pure-function regressions in work-panel-resize.test.mjs.
  • Store regressions in the new work-panel-width-preference.test.mjs.
  • An 866px viewport scenario in scripts/e2e-three-column-layout.mjs.

Validation

Candidate: 5a8ae904f1c0324473260523f653fcda1f923535
Base main: 4f9f051e54c495ac0c5164f2ef4dd687c704bc11
Environment: Windows 11 (10.0.26200), Electron 43.6.0, Node
24.14.0, Rust 1.90.0.

• The new layout checks fail against unmodified upstream product code:
  {"width":131} is stored, the panel stays at 131px after the sidebar
  collapses, and the drag reaches 1px. All four pass on the candidate.

• pnpm test:e2e:layout: 82 passed on the candidate. The same 9 checks
  fail on the candidate and on unmodified upstream: the four darwin-only
  preview-header geometry checks and the sidebar group reload/fold sequence
  that ends in nextKey.

• The new store regressions fail against the unmodified work-panel slice
  (4/4) and pass with the fix.

• 49/49 tests passed in work-panel-resize.test.mjs,
  work-panel-width-preference.test.mjs and work-panel.test.mjs.

• Full desktop node --test: 4,005 of 4,076 passed and 8 were
  skipped. The 63 failures are in files that failed the same way on an
  unmodified upstream run on this machine (f21c550e7):

  • remote-host SSH and sh transports;
  • macOS release and signing;
  • provider catalog tests that read the bundled snapshot through
    new URL(...).pathname;
  • POSIX permission modes;
  • the S3 settings timeout.

  sidebar-pinned-rendering also fails against the unmodified product code
  at 4f9f051e5. chat-links-performance failed only under the parallel
  run and passes on its own.

• Workspace build, Desktop typecheck, Biome lint, style tokens,
  architecture budgets, agent-policy and git diff --check passed.

• Documentation checks passed for 86 English/Chinese pairs and
  578 pages.

• Manual pointer testing on an isolated fork build that carries the same
  product change: the reopen width was never stored. The only stored widths
  were the tester's own drags, 365px and then 244px.

E2E entry points

scripts/e2e-three-column-layout.mjs

The layout E2E launches the built app with throwaway profiles. The 866px case
uses CDP viewport emulation, so the native window keeps its size. No provider,
account or user profile is involved. These results do not claim macOS/Linux
runs or installer packaging.

Scope

• The reopen priority itself is unchanged: the panel still yields first and
  MainChat lands on 460px. Auto-collapse and restore, preview mode and native
  window behavior are also unchanged.
• The lent width is runtime-only. There is no new persisted key, and no IPC,
  host or schema change. The only persisted difference is that
  pi.desktop.workPanel never stores, and never loads, a width below 244px.
• Keyboard resizing: a key that cannot move the separator now commits nothing.
  Previously it rewrote the same width.
• No version, dependency or release changes. No profiles, logs or local
  artifacts are included.

Review

Suggested reviewer focus:

• Loan lifetime: only a constrained manual reopen sets the loan. A fully
  collapsed sidebar, by any path, or an explicit resize ends it. It survives
  panel close/open and session switches while the sidebar stays expanded.
• Space returning: extra client width goes back to the panel first, up to
  its preferred width, while MainChat stays at 460px. A narrower window keeps
  the lent width until it no longer fits; then the sidebar yields as before.
• Gesture floor: 244px, or the shown width when narrower, so a press never
  jumps and a drag never reaches a sliver.
• Sidebar budget: while the panel's width is lent, the sidebar resize range
  uses the shown panel width, as it did when the squeezed width was stored.
• Existing profiles: a stored width below 244px, which only the old reopen
  path could write, loads as 244px.

[vastsa]

Thanks for the focused fix and for documenting the narrow-window reproduction. I verified the 866px reopen/restore path, the persisted preferred width, and the 244px drag floor on the latest-main integration candidate. The targeted panel tests passed (22/22), the layout E2E passed (205/205), the updated PR CI and Docs checks are green, and the PR-base gate passed. Merged as e219a3e.