fix(term): defer controller resync until terminal data is loaded

[kruux]

Fixes #3162

Problem

With fish as the shell, every new terminal tab printed could not read response to Primary Device Attribute query after a 10-second delay. fish sends a DA1 query at startup and waits for the terminal's reply.

Root cause

TermWrap.handleTermData drops xterm.js replies while loaded is false. The shell is started by resyncController("initial resize"), which can run before initTerminal() finishes loading the initial terminal data, so fish's DA1 reply is discarded and fish waits out its timeout. It is a race, so it depends on timing.

Fix

A resync requested before the terminal is loaded is held in pendingResyncReason and run once loading completes.

Testing

Linux, fish 4.9.3, local dev build:

• Time to first prompt in a new fish tab: ~10,000 ms before, 17-43 ms after, warning gone.
• Covers fresh launch, rapid successive tabs, and restart with existing tabs.
• bash is unaffected (14-25 ms before and after).
• The reload replay guard from 95b1767 still holds: 0 input frames replayed on reload.

Repro

Set fish as the shell and open a new tab; the warning appears after about 10 seconds.

Alternatives considered

• Resyncing at the end of initTerminal() fixes the same tests but misses TermResyncHandler, which fires on SSH/WSL connection changes, and can start the shell before the element is sized.
• Replaying heldData does not fix it; the replies are dropped, not buffered.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Advanced

Run ID: 8e6cdf40-69fb-4299-acc4-b39b6580fa6f

📥 Commits

Reviewing files that changed from the base of the PR and between a4447c1 and 23ad2e9.

📒 Files selected for processing (1)

• frontend/app/view/term/termwrap.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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Walkthrough

TermWrap now stores a resynchronization reason when the terminal is not loaded. After initial terminal data loading completes, it marks the terminal as loaded, clears the stored reason, and asynchronously calls resyncController. This preserves responses to shell startup queries such as fish’s Primary Device Attribute query.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Severity of issue fixed: Medium

Merge Risk: ⚪ Minimal · up to 23ad2

The deferred resynchronization change has no identified merge-blocking risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: delaying controller resynchronization until terminal data is loaded.
Description check	✅ Passed	The description directly explains the fish shell startup issue, root cause, fix, testing, and alternatives. It is fully related to the changeset.
Linked Issues check	✅ Passed	Issue #3162 requires support for fish's Primary Device Attribute query without the compatibility warning or the startup delay. In frontend/app/view/term/termwrap.ts, resyncController defers reques…
Out of Scope Changes check	✅ Passed	The reported change is limited to frontend/app/view/term/termwrap.ts. The new pending-resync state and deferred replay directly support the fish startup fix in issue #3162. No unrelated change is id…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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