emrg: a tool-call group flips open and closed at every tool boundary, so the transcript jumps on every call #2355

Observed

On master (ccd950b4), a tool-call group's expansion state flips at every tool boundary, so the block's height oscillates between one line and N lines once per call.

emrg/gui/renderer/src/lib/transcript.ts, updateToolGroup:

• line 272 — group.collapsed = !group.userExpanded; when the group holds two or more rows and none is running, i.e. every tool_end collapses the group;
• line 277 — group.collapsed = false; in the else branch, and line 483 — handleToolStart sets g.collapsed = false; when appending to an existing group, i.e. every tool_start re-expands it.

With five calls the content swings between one line and five lines five times.

userExpanded does not prevent this: it only protects a group the host expanded by hand. A group nobody touched still collapses at every tool_end, and a group the host collapsed is re-expanded by the next tool_start (line 483) — the opposite of what the flag reads like.

The existing tests assert the flip as correct, which is why a green suite hides it: emrg/gui/renderer/src/lib/transcript.test.ts expects group.collapsed to be true after the third tool_end with no click in between, and components/TranscriptView.test.tsx asserts the collapsed class on the rendered group in the same situation.

Where observed: this repository, 2026-10-17.

Expected

A group's expansion state changes when the host clicks its bar, and at no other time.

• The state is decided once, when the group is created. A new group starts expanded, because a running tool must stay visible.
• Tool start, tool end and row appends update the bar's count and total time in place and never touch the expansion state — including the case where the group is currently collapsed.
• The bar is one line: give it a fixed row height, so a label growing from "3 tools" to "12 tools" cannot reflow the block.
• No automatic collapse at any point. A collapse when the turn ends would be acceptable as a deliberate single transition, but it is not added here: the strict reading of the rule is one transition per click.

A related half that is already correct

Auto-scroll during a turn is not part of this defect: TranscriptView.tsx:83 scrolls only when the viewport is within 40px of the bottom, so a host who scrolled up is not yanked back on every tool event. That half stays as it is.

Acceptance

Run a turn with five consecutive tool calls and sample a height proxy — the visible row count plus the bar — at every tool_start and tool_end. It must be monotonically non-decreasing; no boundary may shrink it. Clicking the bar once must be the only transition in the sequence, and after that click a further tool_start must leave the group collapsed.

Both tests that assert the old flip must be rewritten, not extended, so the rule is pinned by a test that fails on the previous behaviour.