feat(tabs): draw lineage lines as one tree for the selected tab's family

Lineage lines used to draw one glowing dashed bezier per parent/child pair,
hanging below the tab strip, for every family at once. With a parent on row 3
of a wrapped strip and ten children below it, the curves crossed every lower
row's tab names and ran through the terminal text.

- One rounded orthogonal tree per spawning tab: every route starts at the
  parent, so siblings share a trunk. 1.5px, solid, 1px dark outline; only a
  working child's branch is dashed.
- Routes run only through the gaps between tab rows, joined by a spine left of
  every row (computeLineageTree/computeLineageRows in constants.js), so they
  never cross a tab or reach the terminal. The vertical rail gets the same tree
  on its existing left track.
- Only the selected tab's family is drawn (what it spawned, plus its parent and
  siblings). Selection redraws, and the strip's size transitionend redraws once
  more, since the active tab widens for ~150ms after the selection redraw.
- The routing room is reserved by .session-tabs.lineage-tree, keyed on whether
  any lineage exists, never on the selection, so a tab switch never resizes the
  header or the PTY.
- Colours stay per spawning tab, now claimed in strip order for every family so
  selection order never decides who gets the skin blue.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -250,7 +250,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 **Run launch synchronization**: the Run entrypoint holds an in-flight lock and disables `#runBtn` for the whole launch (≥500ms) so a double click cannot create duplicate `w<n>-<case>` sessions; `_ensureCreatedSessionVisible()` runs before `selectSession()` and `_onSessionCreated()` stays an idempotent upsert, so POST-first and SSE-first both render exactly one tab. ⚠️ **Closing has the mirror-image race**: `closeSession()` must read `wasActive` BEFORE its `await` and announce the delete via `_closingSessions`, and `_onSessionDeleted` skips the active-session handoff for ids in that set; never read `activeSessionId` after the fact. The fallback picks the first `sessionOrder` entry still in `sessions`. Tests: `test/session-close-fallback.test.ts`. → [architecture-invariants#run-launch-synchronization](docs/architecture-invariants.md#run-launch-synchronization)
 
-**Session lineage lines** (tab → tab it spawned, `sessionLineageLines`, per-device, desktop default ON): a create request may name its spawner via a `parentSessionId` body field or the `X-Codeman-Parent-Session` header; `resolveParentSessionId()` (route-helpers.ts) resolves it (exact id or unique ≥8-char prefix, live, visible, same owner) and ⚠️ anything unresolvable is DROPPED, never a 400. Rides `toState()`, no new SSE event. ⚠️ Rendering is a LAYER on the existing SVG pass (`_appendLineageConnectionLines` at the tail of `_updateConnectionLinesImmediate()`), geometry pure in `computeLineagePath()`: one U-bridge shape hanging from the strip bottom, colors keyed on the SPAWNING tab and memoized (never by draw index). ⚠️ Desktop only (z-index vs the fixed mobile header). ⚠️ Paths must keep `data-agent-id="lineage:<childId>"` (the entrance animation queries it); skip edges whose endpoint is scrolled out of the strip. → [architecture-invariants#session-lineage-lines-tab--tab-it-spawned](docs/architecture-invariants.md#session-lineage-lines-tab--tab-it-spawned)
+**Session lineage lines** (tab → tab it spawned, `sessionLineageLines`, per-device, desktop default ON): a create request may name its spawner via a `parentSessionId` body field or the `X-Codeman-Parent-Session` header; `resolveParentSessionId()` (route-helpers.ts) resolves it (exact id or unique ≥8-char prefix, live, visible, same owner) and ⚠️ anything unresolvable is DROPPED, never a 400. Rides `toState()`, no new SSE event. ⚠️ Rendering is a LAYER on the existing SVG pass (`_appendLineageConnectionLines` at the tail of `_updateConnectionLinesImmediate()`) and draws ONLY the selected tab's family (what it spawned, and the family it was spawned into), so a selection change must redraw (`_updateActiveTabImmediate`, gated on `_lineageTotalEdges`), and again on the strip's size `transitionend` (the active tab widens for ~150ms after the redraw). Geometry is pure in `computeLineageTree()`: one rounded orthogonal tree per spawning tab, every route starting at the PARENT (siblings share the trunk exactly), routed ONLY through the gaps between tab rows plus a spine left of every row, so it never crosses a tab or the terminal. ⚠️ That room is reserved in CSS by `.session-tabs.lineage-tree` (`_syncLineageGutter()`, called before the wrap is measured), keyed on whether ANY family exists, never on the selection, or every tab switch would resize the header and the PTY. Colors are keyed on the SPAWNING tab, claimed in strip order for every family, and memoized (never by draw index or selection order). ⚠️ Desktop only (z-index vs the fixed mobile header). ⚠️ Paths must keep `data-agent-id="lineage:<childId>"` (the entrance animation queries it); skip endpoints scrolled out of the strip. → [architecture-invariants#session-lineage-lines-tab--tab-it-spawned](docs/architecture-invariants.md#session-lineage-lines-tab--tab-it-spawned)
 
 **Auto-named sessions** (`autoNameSessions`, SYNCED, default OFF): a placeholder tab (`w3-myapp`) takes its first real prompt as a title in the `<prefix>: <title>` form, so the case identity and `w<n>` counter survive. Ownership is `SessionState.nameSource` (`placeholder` | `auto` | `manual`; the `name` setter / `PUT /api/sessions/:id/name` makes it `manual`, never touched again). ⚠️ `applyAutoName()` flips to `auto` even if the string is unchanged, so only the FIRST titled prompt names the tab. ⚠️ Only user input counts: `SessionWriteOptions.fromUser` is set by the browser WS path and `POST /api/sessions/:id/input` ONLY; any new user-input path must set it (and the send-key Shift+Enter path must call `trackUserInput()`). ⚠️ The pure tracker (`session-auto-name.ts`) sits on the raw keystroke stream with an explicit rule per key; add a rule for any new key class. ⚠️ `nameSource` also decides `--name`: only a `manual` name is pinned on the claude CLI (`Session.cliPinnedName`), since `--name` is also the `/resume` title; a rename appends a `custom-title` row to a LOCAL, non-docker transcript, and a same-name PUT is a no-op (never flips to `manual`). Tests: `test/session-auto-name.test.ts`. → [architecture-invariants#auto-named-sessions-first-prompt--tab-title](docs/architecture-invariants.md#auto-named-sessions-first-prompt--tab-title)