[ark] Multi segment journeys

[paullewis]

What

Fixes multi-step journey bugs and adds missing lifecycle states: themed processing indicator, step navigation between segments, a completion view for finished journeys, and graceful error handling with retry for Gemini 503s.

Why

Journeys were broken in several ways: steps didn't advance visually, the step counter went past total ("4 of 3"), the processing spinner was invisible, the last step's emit locked users out, and API errors silently killed the journey.

Changes

Backend (journey_router.py, world_model.py, main.py)

• Added error_message field to Journey with human-friendly 503/429 messages
• Capped step counter: min(current_step_index, len(steps))
• Added retry_journey() — resets a failed journey to planning and re-triggers generation
• Added POST /journeys/{id}/retry endpoint
• Wired on_progress callback into _call_agent for real-time agent progress
• Filtered artifact copying to .jsx/.css only

Frontend (ark-app.ts, journey-store.ts, backend.ts)

• ViewManager cleanup: null out #viewManager when viewport DOM is removed, fixing step 1→2 transition
• Completion view: themed panel showing journey objective + accumulated context, with "Done" button
• Error view: ⚠️ icon + error message + "Retry" button, works both in-flight and from the listing
• Inspector removed from journey viewport (kept for runs)
• Spinner theming: processing indicator uses --cg-* tokens, theme CSS injected into shadow DOM via :root→:host remap
• Reuse 404 fixed: added source: "journey" to ViewBundle, inspector skips reuse check for journeys
• Increased polling timeout to 5 minutes
• Completed/errored journeys are reopenable from the listing

Types (types.ts)

• Added source?: "run" | "journey" to ViewBundle

Testing

1. Start a new journey — spinner should show with theme-aware colors and real-time progress text
2. Complete all steps — completion view should show accumulated context with "Done" button
3. Reopen a completed journey from the listing — should show the completion view
4. Kill the backend mid-generation or wait for a 503 — error view should appear with "Retry" button
5. Click Retry — should reset and re-trigger generation
6. Switch themes during processing — spinner should follow the active theme

[github-actions]

📊 Coverage Report

Metric	PR	Main	Delta
Lines	98.30%	98.30%	⚪ +0.00%
Functions	98.25%	98.25%	⚪ +0.00%
Branches	94.17%	94.17%	⚪ +0.00%