feat(components): loading states and a cached conversation in its first frame

[zxch3n]

Related issue

Problem / pressure

Opening a conversation showed a blank pane, a cached conversation flashed a skeleton, and switching between conversations already in memory painted three blank frames (~125ms).

Summary

• Skeleton only when nothing is cached locally, decided after the IndexedDB read; "Updating" in the info bar while a cached copy catches up (after 400ms, at least 500ms).
• ManagedStoreCache.peek / peekSessionStore let useSessionDoc render an open store in its first commit; useTurnRange is ready in render once hydrated.
• The reveal writes visibility directly, and own scroll writes dispatch scroll so Virtua renders the new range in the same frame.

Visual explanation

sequenceDiagram
  participant K as Click
  participant R as React commit
  participant P as Paint
  Note over K,P: Before — 3 blank frames
  K->>R: mount; await acquire(store)
  R->>P: empty pane
  R->>P: hidden (tail ready after a promise tick)
  R->>P: hidden (reveal deferred)
  R->>P: conversation
  Note over K,P: After
  K->>R: mount with peeked store; range hydrated ⇒ ready
  R->>P: conversation (first painted frame)

Loading

Before / after

Before	After
In-memory switch: 3 blank frames	Conversation in the first painted frame
Cached conversation flashes a skeleton	Skeleton only when nothing is cached

Test plan

• packages/components: tsgo clean; vitest 4060 passed on this layer; docs check clean.

🤖 Generated with Claude Code

[github-actions]

Desktop PR regression failed on commit 5cac4c47ff98896d17fb64e8bc94fb3fddb1fdb4.

• Workflow run: https://github.com/LodyAI/Lody/actions/runs/35954686770
• Failed scenarios indexed: 0
• Recording: 1/1

Recordings not attached

• Run evidence: failure-index.json is missing

The Actions artifact retains the complete trace, screenshots, logs, and runtime evidence.

[github-actions]

Desktop PR smoke regression failed on commit 357660045cb83d520d742e2d51481d6bddd5dd7e.

• Workflow run: https://github.com/LodyAI/Lody/actions/runs/35959080412
• Failed scenarios indexed: 0
• Recording: 1/1

Recordings not attached

• Run evidence: failure-index.json is missing

The Actions artifact retains the complete trace, screenshots, logs, and runtime evidence.