fix(opencode): coalesce stream updates and add reconnect backoff

[chindris-mihai-alexandru]

Summary

This PR narrows the scope to surgical TUI performance fixes in the existing OpenTUI path. It focuses on stream event coalescing, reconnect backoff, and lower-cost part updates during streaming.

Related to #13027.

What Changed

1) Redraw coalescing for stream updates

• File: packages/opencode/src/cli/cmd/tui/context/sdk.tsx
• message.part.updated events now use a slightly longer batch window than non-stream events.
• Non-stream events still flush quickly.
• Added a queue cap that forces an immediate flush to avoid unbounded backlog.

2) Idle CPU guard for SSE reconnects

• File: packages/opencode/src/cli/cmd/tui/context/sdk.tsx
• Added reconnect delay/backoff after stream failures.
• Added a short pause after stream completion before reconnecting.
• This avoids tight reconnect loops when the stream drops repeatedly.

3) Lower-cost stream part updates

• File: packages/opencode/src/cli/cmd/tui/context/sync.tsx
• For existing parts, use direct replacement instead of reconcile(...) on every message.part.updated event.
• Skip no-op replacement when object identity is unchanged.

4) Stream append path optimization in message rendering

• File: packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
• Removed per-render trim() calls on streaming text content.
• Reused a memoized content accessor for markdown/code renderables.
• This avoids repeated full-string scans/copies as streamed text grows.

Why This Scope

The previous branch attempted a broader architecture path. This version keeps the implementation in the current renderer/data flow and addresses known hotspots directly.

Notes

• No new rendering subsystem.
• No framework rewrite.
• No behavior change to message ordering or event semantics.
• The branch now contains a single focused commit touching 3 files.

Related Context

These changes align with common TUI guidance to avoid continuous redraw pressure and busy reconnect loops:

• Ratatui high draw-rate CPU issue (terminal.draw): Extremely high CPU usage of the terminal.draw method ratatui/ratatui#1338
• Streaming markdown optimization via partial updates (Will McGugan): https://willmcgugan.github.io/streaming-markdown/

Validation

I ran local typecheck, but the workspace currently has many unrelated baseline errors in this environment. The changes in this PR are small and isolated to TUI event/render paths.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

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No duplicate PRs found

[pkuxkxjason]

Please merge this PR. I am suffering for the performance issue of TUI everyday!

[chindris-mihai-alexandru]

hey @thdxr @rekram1-node @adamdotdevin - I think this is worth taking a look at and would greatly benefit the OpenCode community. Lmk your thoughts / suggestions / objections.

[github-actions]

Hey! Your PR title perf(tui): coalesce stream updates and add reconnect backoff doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[chindris-mihai-alexandru]

I narrowed this PR to a surgical scope and force-pushed the branch.

Current diff is only 3 files in existing TUI paths:

• packages/opencode/src/cli/cmd/tui/context/sdk.tsx
• packages/opencode/src/cli/cmd/tui/context/sync.tsx
• packages/opencode/src/cli/cmd/tui/routes/session/index.tsx

The changes focus on:

• stream event coalescing,
• reconnect backoff to avoid busy loops,
• lower-cost updates for message.part.updated,
• removing per-render trim() in streaming text rendering.

No new rendering subsystem is introduced in this version.