Nice work threading the optional-profile case through the viewer. The selectProfiles extraction plus its three new tests (no-circuit-profile kept, unrecognised files dropped, oldest-first sort) pin down the behavior cleanly, and gating ProfilerDiagram + the search input + the Top-nodes tab on hasProfile avoids any undefined access in the render path. Pane sizing switch (55/20 vs 15/8) via $derived reads well.

A few observations, none blocking:

1. Unrelated formatting churn in Actions.svelte and status.spec.ts. Both files are pure line-wrap reformats that have nothing to do with optional circuit profiles. In a linear history this makes the "why did this line change?" archaeology harder later. Prefer a separate style/formatting commit next time (or drop from this PR).

2. Removal of currentTab = 'Metrics' on node click (SupportBundleViewerLayout.svelte, around the onNodeClicked handler). Previously, inspecting a node auto-switched the analysis tab to Metrics; that side effect is now gone. Intentional? It's not mentioned in the PR description, and it changes UX for the has-profile path — orthogonal to the stated goal. Worth a line in the commit body if intentional, or restoration if not.

3. $effect rewrite dropping the if (!diagram) return guard is fine because diagram?.showGlobalMetrics(true) is null-safe, but the effect now also resets tooltipData and lastNodeData on every profile change — a subtle behavior change beyond "make diagram optional". Fine, just worth calling out in the commit message.

4. Commit message is a single-line subject for a change that touches nontrivial reactive behavior. Subject is descriptive so I won't block, but a short body explaining why the tooltip/lastNode reset was added and why the Metrics-tab auto-switch was removed would earn its place in main's linear history.

Approving — the core change is small, well-tested, and the manual test coverage across tabs is called out. Consider the notes above before the merge (especially #2).