[guan4tou2]

The last open item in DESIGN-core-and-capture.md §6: the timeline's eight flat
toolbar toggles and its eighteen lanes. Both were "problems" with no decision —
and the timeline is the product's most complex, most fragile screen, so the
approach was picked before building (a prior three-view-modes attempt was
reverted for inventing personas).

Toolbar toggles — grouped, rare ones behind "More"

The eight toggles sat in one undifferentiated row mixing three kinds of control
(time/axis, filter, view). Not the reverted approach — no modes or personas.
The low-frequency view/audit controls (session dividers, timezone, auditor
view) move behind a single More popover; the high-frequency ones stay in the
row where they cluster. The auditor view in particular was worth demoting — it
hides the logged tier to show the chained chain, a tamper-evidence concern the
core revision moved off centre.

18 lanes — banded by capture group

Lanes now group into the same commands / traffic / artifacts bands the
readiness card uses, plus a signals band for the derived/alert lanes. A band
opens collapsed to one row whose dots keep their per-lane colour, and expands to
its member lanes on click. Default all-collapsed: the timeline opens as three or
four bands, not eighteen. Band-collapse is project-scoped, like lane visibility.

Under the hood this is a row-key abstraction over the existing geometry — a row
is a band id (collapsed) or a lane id (expanded) — so every site that keyed on a
lane now keys on the row, while dot colour still comes from each event's own
lane.

The crash the e2e caught

The project-scoped band-load effect referenced projectIdForKeys in its
dependency array while sitting above that const's declaration — a
temporal-dead-zone throw during render, in the esbuild-bundled app only, that
vitest's source transform never saw. Same class as the TargetView crash from
PR #23, caught the same way: app-in-the-loop. Moved below the declaration.

Verification

• npm test — 847 passed
• npm run e2e — 63 passed, including two new specs that verify, in a
  running app, that the overflow hides/reveals the rare controls and that the
  timeline opens banded, still draws its events collapsed, and expands on click.
• Screenshot of the banded timeline attached to the branch.

🤖 Generated with Claude Code

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