Fix/panel scrollback leak 457

[ilijachrchev]

Description

Fixes #457 — new Claude Code tab receives another panel's mangled screen buffer as its first prompt.

Panel-scrollback readers sourced text from the raw PTY append log (terminal.scrollbackBuffer) and merely ANSI-stripped it. The append log accumulates every repaint frame — agents and tools update in place via cursor-motion escapes (\x1b[nD, \x1b[K, column addressing), not carriage returns. sanitizeTerminalOutput only collapses \r-based overwrites, so cursor-motion fragments concatenate into the reported garbage ("Workingorking•rking•king•ingngg"). The default 500-line copy preset ≈ the reported 9–12 KB.

The codebase already knew the raw log is unreliable — getTerminalState and agent-status detection both use the screen emulator instead. Three consumers shared the defective raw-log path:

1. runpane panels output → getPanelScrollback (main/src/ipc/runpane.ts) — the context-capture path; its output flows into --initial-input-file, prepended to the typed "continue"
2. terminal:getScrollbackClean (main/src/ipc/panels.ts) — the UI @-terminal raw-copy feature
3. terminal:save-scrollback (main/src/ipc/panels.ts) — the @-terminal embed-copy feature

The fix routes all three through a new getScrollbackText() method on the screen emulator, which renders clean plain text from the already-correct rendered buffer.

Changes:

• TerminalStateEmulator.getScrollbackText(maxLines?): clean plain text from the rendered buffer (scrollback history + viewport), trimming trailing blanks before applying the line limit
• TerminalPanelManager.getCleanTerminalScrollback(panelId, maxLines): awaits emulator idle, returns clean text or null (no live emulator → caller falls back to persisted state)
• Routed both panels.ts IPC handlers through the emulator, keeping the sanitized persisted-state fallback for lazy/inactive terminals
• Routed runpane panels output through the emulator (made panelScrollbackOutput async)
• Tests: emulator renders in-place cursor repaints as clean text, line-limit trimming, and a runpane integration test asserting the emulator source wins over the raw log

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Code refactoring

Checklist

• I have read the CONTRIBUTING.md guidelines
• My code follows the code style of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have run pnpm typecheck and pnpm lint locally
• I have tested the Electron app locally with pnpm electron-dev

Critical Areas Modified

• Session output handling (requires explicit permission)
• Timestamp handling
• State management/IPC events
• Diff viewer CSS

Screenshots (if applicable)

N/A — the bug produces no visible UI change; the symptom is in the agent's session JSONL (first user message contains another panel's screen dump). The fix changes what text the scrollback readers return internally.

Additional Notes

• pnpm run typecheck passes. OxLint exit 0, ESLint 0 errors in touched files.
• terminalStateEmulator.test.ts (9), runpane.test.ts (60), terminalPanelManager.test.ts — all pass.
• Two non-code failures (Knip's zod/mini resolution; daemonRegistryBindings minimatch CJS/ESM) reproduce identically on the base commit — pre-existing, not from this change.
• Manual end-to-end testing was not performed — the dev Electron app shows "Open Pane from the desktop app" on both this branch and plain main (v2.4.62), a pre-existing Windows dev environment issue unrelated to this @fix.
• One pre-existing typecheck error on the base commit (runpane.ts:475 PaneCommandValue) was fixed as part of the rebase cleanup (cast request as PaneCommandValue).