feat(opencode): add AI psychosis detector with heartbeat-based instance tracking

[Aditya190803]

Issue for this PR

Closes # (no issue — feature request from discussion)

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds an opt-in "AI psychosis detector" that warns users when they have too many opencode instances running for too long.

Each process writes a heartbeat file to ~/.config/opencode/instances/{runID}.json on startup. On check, it scans all live heartbeat files and computes severity based on instance count and duration. Cleanup happens on exit / SIGTERM; stale files (>48h) are automatically filtered.

Warnings escalate through four tiers:

• mild (3+ instances or 12+ hours): playful tone
• concerned (5+ instances or 12+ hours): "you might want to step away"
• worried (8+ instances or 24+ hours): "we are genuinely concerned"
• urgent (10+ instances or 48+ hours): wellness check

Delivery varies by mode:

• CLI non-interactive: printed to stderr before the prompt
• Split-footer interactive TUI: printed before the runtime lifecycle starts
• Full TUI: toast notification, guarded by a Ctrl+P palette toggle (app.toggle.psychosis_detector)

The feature is disabled by default. Enable via opencode.json:

{ "psychosis_detector": { "enabled": true } }

How did you verify your code works?

• bun typecheck passes cleanly
• All 91 existing config tests pass
• Changes are scoped to only the new feature files and the integration points

Screenshots / recordings

N/A — CLI/TUI feature, no visual changes to existing UI.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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