v0.9.x: implement true full-screen runtime parity before making live room default

[spytensor]

Context

The intended product shape is still one full-screen CoreRoom room, but the current live-room bridge is only a staged renderer/router. Before it can become the default again, it must own the same execution guarantees as cr start.

This issue tracks the larger parity work that is intentionally not part of the v0.9.7 hotfix.

Acceptance Criteria

• AC-1: Full-screen live room spawns configured role engines or reuses the same runtime session manager as cr start.
• AC-2: Bare text and explicit @role dispatch produce real role turns and durable CREP/message events.
• AC-3: Streaming role output, thinking/working status, tool counts, and work cards render in-room while turns are active.
• AC-4: Permission prompts use the mature permission IPC/socket path inside the full-screen surface.
• AC-5: /halt, Ctrl-C handling, /fresh, /refresh, /resume, /transcript, /journal, and /patch are either implemented in-room or explicitly blocked with parity tracking.
• AC-6: PTY dogfood covers a real authenticated engine turn or a deterministic local fake engine that proves the same runtime contract.
• AC-7: Only after AC-1 through AC-6 pass may plain cr default to the full-screen live room again.

Required Evidence

• Runtime integration tests or a deterministic fake-engine dogfood harness.
• Real PTY evidence for active turn status, permission prompt, completion, and durable transcript state.
• Updated architecture docs and threat model.

Non-goals

• Shipping as part of v0.9.7.
• Treating dashboard/rendered prose as completion evidence.

Tracker Update Required

This issue must remain future-scoped until a concrete implementation plan and release gate exist.

[spytensor]

User report after v0.9.7: plain cr is truthfully executable but visually/product-wise still feels like the old pre-full-screen runtime. Treat this as active blocking work: the next fix must make the default path a real full-screen Control Room runtime, not a staged preview and not the classic REPL splash. v0.9.7 is an emergency truthfulness rollback, not the desired endpoint.