fix: restore agent input after full restart

[DeadWaveWave]

💡 Change Scope

• Small Change: Fast feedback, localized UI/logic, low-risk.
• Large Change: New feature, cross-boundary logic, runtime-risk (persistence, IPC, lifecycle, recovery).

📝 What Does This PR Do?

This PR merges the terminal-recovery branch on top of main and keeps the split TerminalNode recovery architecture while carrying forward main's newer terminal/workspace changes.

User-visible outcomes:

• restore full-restart agent input reliably after cold start
• keep durable placeholder/history behavior aligned with restart recovery
• preserve OpenCode embedded theme synchronization in the split runtime session path
• move debugging specifics into docs/cases/* so docs/DEBUGGING.md stays reusable

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🏗️ Large Change Spec (Required if "Large Change" is checked)

1. Context & Business Logic

This change is about restart/recovery correctness across Main, Preload, Renderer, persisted workspace state, and live PTY sessions. On a full app restart, restored terminal/agent nodes must show durable history immediately, drop stale runtime ownership, attach to a fresh live session, and remain interactive once recovery finishes. The merge also preserves OpenCode-specific embedded TUI theme sync so the split terminal runtime stays behaviorally equivalent to the newer main branch behavior.

2. State Ownership & Invariants

• Main process owns live PTY/runtime session identity; the renderer must not keep sending input to a stale pre-restart sessionId.
• Persisted workspace state owns durable placeholder/history; it may render before runtime recovery completes, but placeholder visibility must not imply ownership of live stdin.
• OpenCode theme bridge messages must only be reported from the active restored runtime path and must not break hydration or alternate-screen behavior.

3. Verification Plan & Regression Layer

Lowest meaningful regression layers used here:

• Unit: tests/unit/app/mainProcessPid.spec.ts, tests/unit/app/useHydrateAppState.helpers.spec.ts, tests/unit/terminalNode/opencodeTuiThemeBridge.spec.ts, tests/unit/terminalNode/opencodeOscColorQueryResponder.spec.ts
• Electron E2E: tests/e2e/recovery.agent-focus-after-restart.spec.ts, tests/e2e/recovery.agent-reopen.spec.ts, tests/e2e/recovery.agent-reopen.gemini-opencode.spec.ts
• Full gate: pnpm pre-commit

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✅ Delivery & Compliance Checklist

• My code passes the ultimate gatekeeper: pnpm pre-commit is completely green.
• I have signed the CLA if required (see CLA.md).
• I have included new tests to lock down the behavior (or explicitly stated why it's untestable).
• I have strictly adhered to the DEVELOPMENT.md architectural boundaries.
• I have attached a screenshot or screen recording (if this touches the UI).
• I have updated the documentation accordingly (if adding a feature or changing a contract).

📸 Screenshots / Visual Evidence

Not attached via CLI. I will add any needed screenshots in the GitHub PR UI.