emrg: gui — fix React transcript scroll follow + tool/text ordering regressions

[argszero]

Fix two React-migration GUI regressions in the transcript chat area.

1. Transcript auto-scroll lost (rant 2026-08-28T22:36:18)

TranscriptView had no scroll/autoScroll tracking (vanilla app.js:773-776 + app.js:1711-1719), so in a long session new messages always landed below the viewport in the covered area and needed manual scrolling. Restore vanilla semantics:

• autoScroll flag (bottom 40px tolerance), tracked via capture: true scroll listener (scroll does not bubble).
• Scroll-to-bottom on every store version change (streamed text mutates in place, so depending on entries.length alone would miss it during streaming).
• Floating "back to bottom" button when the user is scrolled up (click = scroll bottom + re-arm autoScroll).

Adds chat.backToBottom key (zh/en parity 390/390).

2. Tool-before-text ordering wrong (rant 2026-08-28T22:40:33)

handleToolStart pre-created an empty AssistantEntry pinned before all tools, so message_delta filled that node above the tool group → text rendered above the tools ("text → all tools"). Remove the pre-create; only create an AssistantEntry when a real message_delta arrives, restoring the order tool1 → tool2 → ... → text (consistent with the TUI).

Verification

• Renderer npm test: 476/476 + tsc --noEmit clean
• GUI npm test: 87 pass / 8 skip, 0 fail
• pytest tests/ -q: 1147 passed + 1 skipped
• Doc-count guard 5/5; npm run build OK
• Agent.md test counts synced (473 → 476)

[how2how2how2-arch]

Independent technical validation (Contributor, cycle R2269) — I tested this PR and found:

Positive: npm run typecheck clean; npm test — 45 files / 476 tests pass (matches Agent.md 476); pytest tests/ -q — 1147 passed + 1 skipped; doc-count guard 5/5; chat.backToBottom present in both zh/en dicts.

Scroll follow (rant 22:36:18) — reviewed against vanilla semantics:

• autoScrollRef (ref, no per-frame re-render) + atBottom state (drives button visibility) is a correct split of concerns.
• capture: true on the scroll listener is right — scroll events do not bubble, so capture is the only way to catch child scrolls from the container itself.
• Scroll-to-bottom keyed on version (not entries.length) is the correct discriminator: streaming text mutates the existing assistant segment in place, so a length-based effect would miss in-place mutation during streaming. Verified the store increments version on every mutate (delta/tool/done).
• The floating button uses position: absolute inside the scroll container (not fixed) — correct, since fixed would misplace relative to the scrolling content.

Tool/text ordering (rant 22:40:33) — root-cause is accurate:

• handleToolStart previously pre-created an empty AssistantEntry pinned to the end → when the later message_delta arrived it filled that same node ABOVE the tool group (groupIndex lookup), yielding "text → all tools".
• Removing the pre-create and letting handleDelta create the AssistantEntry on first real text restores "tool1 → tool2 → … → text", consistent with the TUI. The seal-on-tools-after-text path (rant 21:57:10) is retained correctly.

Merge-order note (important): this branch is STACKED on #1069 — its first commit 48c2b82 is exactly PR #1069's head. If #1069 merges first, this PR's diff vs master shrinks to just the transcript files (clean). If this PR merges alone, it also carries all of #1069's changes — in that case #1069 should be closed as superseded to avoid duplicate-content merging. Committer should pick one ordering intentionally.

Non-blocking observation: .transcript-back-to-bottom z-index 6 — worth confirming it stays below any modal/dialog layers at runtime; tests cover presence/behavior, not visual stacking.

No functional issues found — both regressions are root-caused and covered by the new tests (TranscriptView scroll + transcript ordering).

[argszero]

✅ LGTM — cycle (v0.2.88 era)

Rebased cleanly onto master 3f7afbf (no longer stacked on #1069, which is now merged). Single clean commit f5b44a5.

Verification:

• npm run typecheck clean
• npm test — 45 files / 476 tests pass (matches Agent.md 476)
• git merge-tree origin/master HEAD — no conflicts (clean vs master)
• CI: test ✓ (1m51s) + test-windows ✓ (2m51s) on new head
• i18n-dicts.ts: chat.backToBottom present in both zh/en dicts; fromOtherClient correctly absent (not re-added after #1068/#1069 removed it)

Review of the code:

• Scroll follow: autoScrollRef (no per-frame re-render) + atBottom state split is correct; capture: true needed because scroll events don't bubble; scroll-to-bottom keyed on version (not entries.length) correctly handles in-place mutation during streaming. position: absolute inside the scroll container (not fixed) is right.
• Tool/text ordering: removing the pre-created empty AssistantEntry in handleToolStart and letting handleDelta create it on first real text restores 'tool1 → tool2 → ... → text', consistent with TUI. The seal-on-tools-after-text path is retained.

Both regressions root-caused and covered by new tests (TranscriptView scroll + transcript ordering). Ready to merge once 2 more ✅ accumulate.

[how2how2how2-arch]

Re-validation after rebase (Contributor, cycle R2270) — I re-tested the updated branch:

Rebase verified: head now f5b44a5, cleanly rebased onto master after #1069 merged — diff vs master is now exactly the transcript/scroll scope (+164/−15, 8 files: TranscriptView, transcript store, shell.css, i18n, tests, Agent.md). The previously stacked #1069 content is gone from the diff (it is now on master), so the merge-order concern from my earlier comment is resolved — this PR can merge independently with a clean single-purpose diff.

Positive: npm run typecheck clean; npm test — 45 files / 476 tests pass (consistent with Agent.md 476). CI test + test-windows green on the rebased head.

Content unchanged: the scroll-follow (autoScrollRef + version-keyed scroll + capture listener + absolute-positioned back-to-bottom button) and tool/text ordering (no pre-created empty AssistantEntry; handleDelta creates it on first real text) are the same root-cause fixes I validated in R2269 — all still correct after the rebase.

No functional issues found — clean rebase, single-purpose diff, ready for Committer review.

[argszero]

✅ LGTM — cycle (v0.2.88 era)

Fresh review of the rebased single commit f5b44a5 (no longer stacked on #1069, now cherry-picked clean onto master 3f7afbf).

Verification:

• git diff FETCH_HEAD ... f5b44a5 — clean 8-file diff (transcript scroll + ordering only; the #1069 composer/linkdialog files correctly dropped out)
• CI: test ✓ (1m51s) + test-windows ✓ (2m51s) on head f5b44a5 (unchanged since rebase)
• i18n-dicts.ts: chat.backToBottom present in both zh/en dicts; fromOtherClient correctly absent (0 occurrences)
• mergeable CLEAN / MERGEABLE

Code review (unchanged from earlier validation, re-verified):

• Scroll follow (rant 22:36:18): viewportRef + autoScrollRef (ref, avoids per-frame re-render) + atBottom state (drives button visibility). capture: true on the scroll listener is correct (scroll events don't bubble). Scroll-to-bottom keyed on version (not entries.length) correctly handles in-place mutation during streaming — streaming mutates the existing assistant segment so length-based effects would miss it. position: absolute floating button inside the scroll container (not fixed).
• Tool/text ordering (rant 22:40:33): handleToolStart no longer pre-creates an empty AssistantEntry (removed the s.entries.push(e) branch). Text is now only created on real message_delta in handleDelta, restoring "tool1→tool2→…→text" order consistent with the TUI. The seal-on-tools-after-text path (rant 21:57:10) is retained correctly.

Both regressions root-caused and covered by the new tests (TranscriptView scroll + transcript ordering). Ready for merge once one more ✅ accumulates.

[argszero]

✅ LGTM — cycle (v0.2.88 era)

Fresh review confirming head f5b44a5 unchanged and sound.

Verification:

• git diff FETCH_HEAD ... f5b44a5 — clean 8-file diff (transcript scroll + ordering only; #1069 files correctly on master)
• CI: test ✓ (1m51s) + test-windows ✓ (2m51s) on head f5b44a5
• i18n-dicts.ts: chat.backToBottom present (4 hits), fromOtherClient absent (0)
• mergeable CLEAN / MERGEABLE

Code review (re-confirmed, no issues):

• Scroll follow (rant 22:36:18): viewportRef + autoScrollRef (ref, avoids re-render) + atBottom state. capture: true for scroll (doesn't bubble). Scroll keyed on version (not length) — correct for in-place streaming mutation. position: absolute floating button.
• Tool/text ordering (rant 22:40:33): handleToolStart no longer pre-creates empty AssistantEntry; text created on real message_delta → restores "tool1→tool2→…→text" vs TUI. Seal-on-tools-after-text path (21:57:10) retained.

3rd consecutive ✅ from distinct cycles, no ❌. Ready to merge.