fix(chat): keep composer drafts across hydration

[waleedlatif1]

Summary

• Composer adopts text typed into the server-rendered textarea before hydration. React dropped those input events, so state stayed empty and the next render wiped the text. This is what made e2e (mobile) intermittently fail draft scroll boundaries on WebKit (The long draft must have a scrollable editor / The draft must overflow its editor): the fill landed before the composer hydrated and the draft disappeared
• A saved draft is restored after hydration instead of in the initial render. Reading localStorage during hydration mismatched the server HTML, so every reload with a saved new-chat draft raised a hydration error and regenerated the composer
• One shared useHydrated hook replaces three private copies (composer, organization home, landing theme toggle)
• Mobile E2E: the draft scroll check waits for the draft to overflow its editor instead of measuring once, and a new check saves a draft, reloads, and requires it back with no hydration error

Type of Change

• Bug fix

Testing

• use-prompt-editor.test.tsx: new jsdom test hydrates server HTML with text typed before hydration (red before the fix)
• Mobile E2E (WebKit desktop) against next dev: 20 consecutive runs, 0 failed checks; before the fix 7/20 failed with the reload hydration error. The new reload check fails on the pre-fix composer. Full suite (Chromium + WebKit, all viewports) 186/186
• bun run lint, bun run type-check, bun run check:audits, bun run test, block registry check

Checklist

• Code follows project style guidelines
• Self-reviewed my changes
• Tests added/updated and passing (new tests pass the test-audit authoring gate)
• No new warnings introduced
• I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

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1 Skipped Deployment

Project	Deployment	Actions	Updated
docs	Skipped		Oct 10, 2026 2:56pm UTC

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge; no blocking issues remain.

Summary

The composer keeps text entered before hydration and restores saved drafts without changing the server’s first render.

• Text typed before hydration stays in the composer.
• Saved drafts return after hydration without replacing new typing.
• The composer, organization home, and theme toggle share one hydration check.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Hydrate composer] --> B{Text entered before hydration?}
  B -->|Yes| C[Keep entered text and caret]
  B -->|No| D[Restore saved draft as a seed]
  D --> E[Restore skill references when skills load]

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_{Reviews (3) · Last reviewed commit: "fix(chat): keep the caret where the user..." · Reviewed by Greptile}

[waleedlatif1]

@greptile

[waleedlatif1]

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[cubic-dev-ai]

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[cubic-dev-ai]

All reported issues were addressed across 7 files

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[waleedlatif1]

@greptile

[waleedlatif1]

@cubic-dev-ai review this PR

[cubic-dev-ai]

@cubic-dev-ai review this PR

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[cubic-dev-ai]

No issues found across 7 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

<sub>Heads up: you’ve reached your flex budget. Increase your flex budget or wait for usage to reset.

Turn on auto-fix | Re-trigger cubic</sub>