[futurepaul]

Closes #797.

The race

#layout starts hidden until the person is signed in.

1. layout.js's first write() measured a grid 0 px wide, found no room for the left pane, and hid the sidebar (display: none without left-open).
2. When showLayout() revealed the grid, the ResizeObserver fitted it again, but through requestAnimationFrame, so a frame later.
3. For that frame every page load showed without its sidebar.

deploying_start_ui read the sidebar's buttons right after it saw the notice change, and now and then landed in that frame:

• chrome: false on sessions: an import writes its archive's search #774's run 41154120681 and its rerun;
• the same on devstack: the front door logs each request and its answer #748's run 41158183481 (e2e flake: shell-ui's deploying start once saw the sidebar's chrome missing (chrome: false) #797).

Fix (cell/shell/layout.js, fitted() only)

A grid that measures nothing has no window to fit, so its sides stay as saved: the sidebar is shown with the page. Its first measure then fits the sides as before, so a window too narrow for both panes still hides the left one.

The check, made exact (crates/e2e/src/lanes/shell.rs)

A script installed before the shell runs (DEPLOY_SEEN) does three things:

• a MutationObserver records what the page shows at the moment its notice first says Updating: the layout shown, the sidebar's Settings and Apps visible, and no release on the page. It reads before any frame is drawn, instead of looking a moment later;
• it collects the console's lines;
• it counts the page's asks of /api/identities/me.

The detail reports each part separately, which answers #797's "which half was false".

Proof (local cargo xtask e2e --only shell-ui)

• Without the fix: the check fails, with first: {"layout": true, "chrome": false, "released": false} (317 passed, 1 failed). Nothing else differs.
• With the fix, three runs in a row: both deploying checks pass every time.
  • Run 3 passed 318/318.
  • Runs 1 and 2 each had one other failure, the Apps card race, which is the open flake e2e flake: shell-ui's Apps card race keeps the old card after closing and reopening Apps #782 (seen on another branch before this change).

cargo xtask check passes.

🤖 Generated with Claude Code

[alexlwn123]

Pass at f9d62de3969664e85edd4645a89175719398ec7c.

The zero-width guard fixes the hidden-grid startup race while preserving saved open/closed choices and the existing fit once the grid is measurable. The regression check captures the first Updating notice in a MutationObserver and reports layout, sidebar visibility, and release-text exposure separately. I traced the startup, resize, narrow-screen, and retry paths and found no blocking regression. The implementation is appropriately small and uses the existing layout and browser-test helpers.

Validation: git diff HEAD^ HEAD --check passed. CI check and all four e2e shards are still pending; I did not run the suites locally. The referenced external engineering-style document was unavailable at its configured path.