refactor(desktop): re-host instance edit as AgentInstanceEditDialog behind AgentDialog (Phase 1B.3b)

[wesbillman]

Summary

Phase 1B.3b of the unified agent model: the instance-edit dialog re-homes into the unified AgentDialog family. EditAgentDialog.tsx becomes AgentInstanceEditDialog.tsx (git mv — the 954-line body is unchanged except the function name), and AgentDialog gains an instance-edit mode, making it the single entry point for all four agent intents: create definition, create definition + start, create standalone instance, and now edit instance.

What changed

• AgentDialog.tsx — props become a discriminated union (AgentDialogCreateProps | AgentDialogInstanceEditProps). instance-edit renders AgentInstanceEditDialog as a pass-through; the create paths are byte-identical, relocated into an internal AgentCreateDialogRouter so hooks stay unconditional. Create callers use the new exported AgentDialogCreateMode type.
• UserProfilePanel.tsx — the single mount swaps <EditAgentDialog …> for <AgentDialog mode="instance-edit" …>. The persistent mount, editAgentOpen state, and the requestOpenEditAgent nudge-event subscription (the only route that opens this dialog) are untouched.
• AgentsView.tsx — create-state type narrows to AgentDialogCreateMode (type-only ripple).
• agentInstanceEditPinning.test.mjs (new) — pins the inherit-toggle → credential-gate → submit seam chain through the pure modules exactly as the component wires them: prospective-runtime resolution from the linked persona (not the stale pin), gate validating the same submission snapshot submit persists (both directions: clears with the persona credential, blocks without it), command-clear sentinel + harnessOverride derivation, and the steady-state-inherit authoritative-edits contract.
• Comment-only renames in CreateAgentDialog.tsx, personaProviderModelFields.tsx, editAgentProviderDiscovery.test.mjs.

Invariants preserved (review pins)

• personaRuntimeModel.ts and useRequiredCredentialState.ts: zero diff.
• The [open, agent.pubkey] reset lifecycle travels inside the moved body untouched — no effect surgery.
• All testids move with the body; edit-agent.spec.ts passes unmodified (zero e2e spec edits — the suite added in test(desktop): add edit-agent dialog e2e coverage (Phase 1B.3b-pre) #1628 is the acceptance gate for this move).

Testing

• tsc --noEmit clean; biome clean.
• Full desktop unit suite: 2067/2067 pass (incl. the 5 new pinning tests).
• playwright --project=smoke edit-agent.spec.ts: 3/3 pass, spec unmodified.
• Scoped smoke slice -g "agent|persona": 59/59 pass.

Part of the Phase 1B UI unification (#1624 → #1626 → #1627 → this). Next: B3c profile-panel cutover deletes the remaining legacy dialog paths.

[wesbillman]

Review (Pinky, per agreed posture) — GitHub approve blocked (same authed account as author), so recording the verdict here.

Mechanical half — all five pins verified:

1. Pure modules: personaRuntimeModel.ts + useRequiredCredentialState.ts zero-diff ✅
2. Persistent mount + editAgentOpen toggle: import swap only; [open, agent.pubkey] reset effect travels inside the moved body intact ✅
3. Nudge contract: consumePendingOpenEditAgent/subscribeOpenEditAgent untouched ✅
4. Frozen selectors: 99%-similarity rename, testids 9↔9, desktop/tests/e2e/ diff = 0 lines, playwright.config untouched ✅
5. Pinning test: 5 tests chain inherit-toggle → gate → submit through the real pure-module exports ✅

Manual half: fresh checkout of 61efb08, edit-agent.spec.ts run unmodified → 3/3 passed (zero-spec-edits acceptance gate met).

Union shape note: TS now enforces open on edit mode only; create paths byte-identical behind AgentCreateDialogRouter — correct shape.

Verdict: APPROVE. Narf!