fix(workspace): complete session-id remap (relationships + pins) at reload/switch sites (#248)

[Juliusolsson05]

From the codebase-wide id-coherence audit you asked for. Closes the remaining incomplete-remap gaps of the same class as #266/#267/#271/#272/#273.

Bug

replaceSession (reload / provider-switch / resume / rewind) and reloadAgentSessions ("reload all") mint fresh session ids but only remapped the tile tree, detached/dispatch focus, and tiled lanes — not:

• SessionMeta relationship pointers (linkedParentId / orchestrationParentId / orchestrationRootId). A linked/orchestration child of a reloaded agent kept pointing at the now-dead parent id → renders top-level, and parent-scoped orchestration MCP reads break.
• pinnedSessionIds — a pinned agent that got a fresh id silently dropped out of the Pinned section.

Only rehydrate handled relationship pointers (via remapSessionMetaRelationships).

Fix

• New neutral module src/renderer/src/workspace/idRemap.ts (avoids a persistence↔actions import cycle), housing the moved remapSessionMetaRelationships plus remapSessionsRelationships (remap pointers across a whole sessions record — so a session whose id changed has every other session's pointer to it updated) and remapPinnedSessionIds.
• Applied both at replaceSession and reloadAgentSessions. rehydrate now imports the shared helper (re-exported there for its historical import path).

Scope / deferrals (deliberate, with rationale)

Kept to the clearly-correct, in-store, unmitigated fixes. Explicitly deferred to their own follow-ups:

• switchProvider malformed synthetic ClaudeEntry (missing uuid/parentUuid/timestamp) — real, but needs the transcript-translation/resume contract investigated first; not a safe ride-along in a state-coherence PR.
• spotlight/reader "follow on remap" — cross-slice plumbing, and already cleared by useSpotlight/ReaderModeSanity (UX polish, not correctness).
• undoClose relationship preservation — deeper issue: restored sessions get their meta from spawn(), which doesn't carry relationship fields at all.
• UiShell transient modal ids (bury/view-prompts/rewind/etc.) — cross-store, low value.

The audit also gave a clean bill to the IPC subscription layer and confirmed no other updateRuntime-class "method called but not exposed" bugs.

Verification

• 0 type errors in any touched file (baseline unchanged at 4 pre-existing).
• Full npm run build green.
• ⚠️ Live confirm after rebuild+restart: reload a parent that has a linked/orchestration child → child stays nested under it; reload a pinned agent → it stays pinned.

No new test files (repo convention).