Task: Fix AI design rapid session switching freeze

Identity

Diagnose and fix the Makelore AI Design client freeze reported when a user rapidly switches Conversations after login.
Keep the change limited to the Renderer task-stream lifecycle and its unit regression coverage; do not change the Works API or persistent Agent Session contract.

Preserve the existing Workspace + Conversation identity and generation guards, including stale-stream isolation and REST reconciliation after the Canvas effect is cleaned up.
Do not issue a second event-stream open for the same active Workspace + Conversation solely because reconciliation was requested while its stream is connecting. An explicit Conversation selection may invalidate the old identity and start the newly selected Conversation's stream. Only a known degraded stream may be forced closed and reopened by reconciliation.
Use a regression test that models an unresolved openImageWorkspaceTaskEvents Promise, because the underlying connection attempt is not cancellable once started.

Confirmed the freeze mechanism: Canvas effect cleanup marks task-stream reconciliation while the stream is still connecting; the next connect call treated every non-connected state as broken, closed the logical stream, and started another request. The old Promise could not be cancelled and only closed its EventSource after eventually resolving, so rapid switching accumulated concurrent connection attempts.
Changed connectTaskStream to force a close/reconnect only for degraded streams. An in-flight connecting stream is reused while Conversation and task REST reconciliation still runs.
Added a store regression test proving reconciliation does not issue a second stream-open request while the first one is unresolved.
Audited the adjacent Main SSE relay close timing; the existing finally path closes a subscription after a response is already closed, and no reliable red test proved an additional leak in this task, so no Main/API change was made.

New regression before the fix: failed as expected (openImageWorkspaceTaskEvents was called twice instead of once).
node_modules\\.bin\\vitest.cmd run tests/unit/image-workspace-store.test.ts --reporter=dot — passed, 1 file / 31 tests.
node_modules\\.bin\\vitest.cmd run tests/unit/image-canvas-page.test.tsx tests/unit/works-square-design-workspace.test.ts --reporter=dot — passed, 2 files / 78 tests. Existing React act(...) warnings were emitted by an unrelated auth test.
node_modules\\.bin\\eslint.cmd src/stores/image-workspace.ts tests/unit/image-workspace-store.test.ts — passed.
node_modules\\.bin\\tsc.cmd --noEmit — passed.
git diff --check — passed.
check_doc_drift.py --task-id 20260819-makelore-session-freeze-7c4e — passed.
Independent Sol read-only final review — PASS. The review noted the untested extreme A→B→A case where a deliberately stalled old open request may later be replaced; that is retained as a separate follow-up rather than part of the same-identity reconciliation race.

Run a real logged-in Electron smoke test that alternates two or more Conversations while the event-stream handshake is deliberately slow; local unit tests prove the duplicate-open race but do not validate a deployed Works gateway or production network behavior.
If production telemetry later shows a WebSocket handshake that never resolves, track a separate cancellation/timeout task instead of coupling it to this Renderer race fix.

None. The fix restores the existing client stream-lifecycle invariant and does not introduce a new architectural decision or canonical contract.