feat(web): Code Mode sub-calls in the trajectory and waterfall views

Trajectory: the layout fold interleaves one subtool cell per sub-dispatch
after its parent Tool cell (assistant-block calls, orphan results, and
running calls alike), indexes sequential across the interleave; settled
durations come from the start/settle pair, running sub-calls show the
em dash. New Sub tag (business tint) + 28px indent.

Waterfall: deriveSubSpans folds the dispatch index into per-turn lanes
with REAL wall time — each parent's window is first start → last settle
and every lane's offset/width is its fraction of it, so parallel
sub-calls visibly overlap; running lanes extend to the window end at
reduced opacity. Lanes draw under the owning turn row.

Both views read codeDispatches through the standard snapshot hook; no
new wire data, replay renders identically to live. Specs pin interleave
order, durations, the running arms, window fractions, and the rendered
lane.

.agents/notes/implemented/feature/2026-07-26-code-mode-trajectory-waterfall-spans.md

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+# Agent Note: Code Mode sub-calls in the trajectory and waterfall views
+
+Status: implemented
+
+English | [中文](2026-07-26-code-mode-trajectory-waterfall-spans.zh.md)
+
+> Scope: the final PR of the Code Mode UI stack — sub-dispatch rendering in the two non-chat views. Chat nesting is owned by the [sub-call rows note](2026-07-26-code-mode-chat-subcall-rows.md); the timing this consumes is the [live-parallel note](2026-07-26-code-mode-live-parallel-dispatch.md)'s start/settle pair.
+
+## Problem
+
+Trajectory and waterfall still rendered a `run_code` turn as one opaque Tool cell / one node-count bar. The chat view got nested sub-rows in the earlier PRs, but the two analytical views — whose whole purpose is structure and timing — showed none of the sub-call structure and none of the per-sub-call wall time the dispatch pair now records. Waterfall sub-spans were deliberately deferred until that pair existed: a span without real timing would have been a lie.
+
+## Decision
+
+**Trajectory: `subtool` cells interleaved after their parent Tool cell. Waterfall: real-time sub-lanes under the owning turn row.**
+
+- **Trajectory**: the layout fold takes the snapshot's `codeDispatches` index; after each Tool cell whose `callId` has dispatches (assistant-block calls, orphan results, and running calls alike), it interleaves one `subtool` cell per sub-dispatch in start order — indexes stay sequential across the interleave. A settled sub-call's duration is its start/settle pair (`durationSeconds(sub.time, sub.callTime)`); a running one shows the em dash, exactly the native in-flight convention. The new cell kind wears a `Sub` tag (business tint) and a 28px indent so nesting reads at a glance.
+- **Waterfall**: `deriveSubSpans` folds the dispatch index into per-turn lanes with REAL timing — each parent's dispatch window is first start → last settle, and every lane's offset/width is its fraction of that window, so parallel sub-calls (PR3) visibly overlap. Running lanes extend to the window end at reduced opacity with a null duration. Lanes draw under the owning turn's bar row, scaled into a fixed lane budget.
+- Both views read `codeDispatches` through the standard snapshot hook — no new wire data, no new stores; replay renders identically to live by construction.
+
+## Alternatives considered
+
+**Fold sub-calls into the turn-span node counts (weight the existing bars).** Rejected: it hides exactly the structure this stack exists to show, and node-count weighting is already flagged as a stand-in (deviation ledger #3).
+
+**A dedicated sub-call panel instead of in-view nesting.** Rejected: the stack's settled UX is nesting under the parent everywhere; a separate panel would diverge from chat and double the selection plumbing.
+
+**Defer waterfall lanes until the P-III duration-lane redesign.** Rejected: the sub-lane timing is real today (the pair), and the fraction-of-window rendering is independent of whatever the turn-level lanes become; deferring would strand the stack's timing payoff.
+
+## Consequences
+
+The waterfall carries the first REAL wall-time rendering in the client (turn bars remain node-count stand-ins — the contrast is deliberate and labeled by hover titles). Trajectory cell indexes now count sub-calls, so `#N` totals grow on Code Mode turns. Specs pin the interleave order and durations, the running em-dash arm, window fractions (offsets/widths), the running-lane extension, and the rendered lane under the turn row.