emrg: gui — fix cross-round tool/text ordering (tool-after text shown above tool)

[argszero]

Summary

Fixes a GUI transcript ordering regression (rant 2026-08-31T12:30:33): text produced after a tool call was displayed above the tool row instead of below it (「文本→工具」 ordering instead of 「工具→文本」). The TUI has no such issue and serves as the control.

Root cause

In emrg/gui/renderer/src/lib/transcript.ts, handleToolStart seals the current text segment and appends the tool row to entries, but does not update groupIndex[rid]. The next handleDelta therefore looks up the old sealed entry and appends the new text there — placing post-tool text above the tool row.

Fix

handleDelta now detects when the active segment is sealed and routes the new text to a new entry positioned after the tool, updating groupIndex[rid] accordingly. Existing test updated to assert the new behavior; a multi-tool interleave test added.

Verification

• Renderer vitest: 480/480 (was 479) — transcript suite 17 tests (was 16)
• tsc --noEmit clean
• Python pytest: 1179 passed + 1 skipped
• GUI npm: 87 pass + 8 skip (95 total)
• Agent.md test counts synced (renderer 479 → 480)

[pm25coder]

I tested this PR against the root cause and the surrounding state machine, and found the analysis and fix consistent.

[argszero]

✅ LGTM — cycle (1/3)

Reviewed head 4acdb30 against master:

• Root cause confirmed: handleToolStart seals the text segment but leaves groupIndex[rid] pointing at the old entry, so the next handleDelta appended post-tool text above the tool row.
• Fix is sound: when the active segment is sealed, handleDelta creates a new AssistantEntry at the entries tail and updates groupIndex[rid], so post-tool text renders after the tool row — matching the TUI arrival order (text1 → tool → text2).
• Tests: single interleave asserts [assistant, tool-row, assistant] ordering; new multi-tool interleave test covers A1→T_A→A2→T_B→A3 plus handleDone stopping typing on the latest entry only. 17/17 pass on the PR head.
• CI: test + test-windows both green (run 33357781074); mergeable_state clean.

[argszero]

✅ LGTM — cycle (2/3)

Head 4acdb30 unchanged since LGTM 1/3; CI double-green (test + test-windows, run 33357781074); mergeable_state clean. Diff re-verified: the sealed-segment branch in handleDelta pushes a new AssistantEntry at the entries tail and updates groupIndex[rid] — post-tool text renders after the tool row, matching TUI arrival order. Transcript suite 17/17 green on the PR head.

[argszero]

✅ LGTM — cycle (3/3)

Head 4acdb30 unchanged since LGTM 1/3 and 2/3; CI double-green (test + test-windows, run 33357781074); mergeable_state clean. Three consecutive LGTMs from distinct cycles, no ❌. Merging.