fix(transparent-stream): defer settled tool-detail DOM + cap per-turn rows (#5966)

[nesquena-hermes]

Closes #5966.

Reported by @curtisszmania-cytocync: chats consuming 28GB+ and freezing the host, "typically when a chat has 15+ user prompts," with Transparent Stream enabled, worst "before the chat fully loads."

Root cause

Transparent Stream never collapses its activity, so the settled render built a DOM node for every activity event of every settled turn at load, and eagerly materialized each tool row's full detail body (tool input/output HTML + Prism/KaTeX/Mermaid post-processing). A 15+ prompt reasoning-heavy history produced thousands of subtrees synchronously → the multi-GB tab freeze. The message virtualizer's unit is messages, not activity rows, and a normal cold load (~30 messages) sits below its 80-row threshold and never engages — so nothing bounded the per-turn row fan-out.

The compact-worklog freeze fix (#5860/#5839) deferred collapsed-worklog DOM, but explicitly did not cover Transparent Stream. This PR is the Transparent-Stream counterpart, reusing the same proven deferral machinery.

Fix (two parts, static/ui.js + static/style.css)

A. Row-detail deferral — a settled, collapsed transparent tool row renders header-only (name, summary preview, status, chevron); its heavy .tool-card-detail body is built on first expand (_materializeTransparentToolDetail). The tool call is recovered from the in-memory stash, or from data-anchor-row-id → S.messages scene after an innerHTML cache round-trip (#5839 recovery pattern). Same anchor-suppressed post-processing as the eager path, so an expanded row is byte-identical. Live and already-open rows are unchanged.

B. Per-turn row cap — a settled turn with > CAP+SLACK (30+10) rows renders only the last 30, behind a clean "Show earlier steps (N)" pill (styled on the existing load-earlier idiom) that materializes the omitted prefix in place with viewport compensation (reader's position held). Exemptions: the just-settled turn (keep-open token — no STREAM_DONE shrink) and any turn already revealed this session. The true Trace tool-count is stashed so "Trace: N tools" stays honest while capped; "Expand all" reveals capped rows first; cache-restore re-wires the affordance.

Server-side #5858 (scene serialize-after-messages) already covers the container-RSS half on the experimental channel; this is the load-bearing browser-DOM half for a Transparent-Stream user.

Evidence

Real-browser measurement (400-tool settled turn, Transparent Stream), master vs this branch:

Metric	master	this PR
Mounted event rows	400	30
Eager tool-detail bodies	400	0
Total transcript DOM nodes	12,494	639 (−94.9%)
Trace label	400 tools	400 tools (honest)

Interactions verified live (0 console/JS errors): "Show 370 earlier steps" reveals all 400 with the previously-visible row held at the exact same screen position (Δ 0px); expanding a deferred row builds only that row's detail; even fully revealed, unopened rows keep their detail deferred.

Crown-jewel streaming RegressionGate: transparent_stream and compact_worklog both CLEAN across the full lifecycle (stream / after-done / switch-away-back / reload-after-done / reload-mid-stream), tool-expand shows input+output, no flicker, no alternating.

Tests

tests/test_issue5966_transparent_stream_lazy_dom.py — 15 tests: source-assertions for both parts + the cache-recovery/count/expand-all/rehydrate wiring, plus a behavioral node-vm harness proving the cap arithmetic bounds mounted rows (400→30) while a normal 12-row turn is never capped (non-vacuity) and the slack boundary (40 uncapped / 41 capped) holds.

[greptile-apps]

Greptile Summary

This PR reduces Transparent Stream DOM usage for large settled conversations. The main changes are:

• Defers settled tool-detail DOM until a row is expanded.
• Caps long settled turns and adds a control to reveal earlier steps.
• Preserves full tool counts and revealed state across renders.
• Adds styling, translations, and tests for the new behavior.

Confidence Score: 4/5

This is close, but the revealed-row recovery issue should be fixed before merging.

• Initially rendered rows and the reveal control now retain the correct scene owner.
• Rows inserted by the reveal loop do not retain that owner after an HTML-cache round trip.
• Affected tool rows can reopen without their input or output in multi-segment turns.

static/ui.js

Important Files Changed

Filename	Overview
static/ui.js	Adds row capping, lazy tool details, cache recovery, and persistent reveal state; revealed prefix rows still omit their scene-owner index.
static/style.css	Adds responsive and reduced-motion styling for the earlier-steps control.
static/i18n.js	Adds singular and plural labels for the earlier-steps control.
tests/test_issue5966_transparent_stream_lazy_dom.py	Covers cap behavior and recovery wiring but does not assert owner metadata on rows inserted by the reveal loop.

_{Reviews (5): Last reviewed commit: "fix(review): extract _transparentToolRow..." | Re-trigger Greptile}

[greptile-apps]

Stamp revealed row owners

Rows inserted by this reveal loop still lack data-anchor-owner-idx. After these rows are saved to the HTML cache and restored, their _deferredToolCall properties are gone. Expanding a revealed tool row in a multi-segment turn can then search the first scene-bearing segment instead of the owning segment, fail to find the row ID, and leave the tool detail empty. Stamp these rows with rawIdx, as the initial settled-render path does.

Suggested change

	if(node){ node.setAttribute('data-earlier-revealed','1'); frag.appendChild(node); }
	if(node){
	node.setAttribute('data-earlier-revealed','1');
	node.setAttribute('data-anchor-owner-idx',String(rawIdx));
	frag.appendChild(node);
	}

Context Used: AGENTS.md (source)

[nesquena]

Review — end-to-end ✅ (approved after two CI-red fixes I pushed)

Independent review of #5966 (@curtisszmania-cytocync): chats consuming 28GB+ and freezing the host with Transparent Stream enabled — the settled render built a DOM node for every activity event of every settled turn at load and eagerly materialized each tool row's full detail body, so a 15+ prompt history produced thousands of subtrees → multi-GB freeze. This is the Transparent-Stream counterpart to the compact-worklog fix #5860/#5839 (which explicitly didn't cover it).

What this ships

static/ui.js (row-detail deferral + per-turn cap), static/style.css, static/i18n.js, tests/test_issue5966_transparent_stream_lazy_dom.py. Agent-authored (nesquena-hermes). MERGEABLE, CI green (18/18 after my fixes).

What I caught — CI was red, two issues, both fixed

1. Locale parity (7d4f7fb8): the new "Show N earlier steps" pill added show_earlier_steps + show_earlier_step_one to the English block only → the strict parity tests (zh/ko/ru/zh-Hant) failed missing-key across CI shards. Added both to all 14 non-English blocks (English fallback, the established convention) after each collapse_all anchor. 197 locale tests green.
2. #5700 harness ReferenceError (197ca695): #5966 added a _transparentToolRowHasDetail(tc) call into _anchorSceneTransparentNodeForRow, but the pre-existing test_issue5700_worklog_event_timestamps node harness (which extracts that render fn) didn't extract the new helper → the extracted fn hit a ReferenceError → 3 #5700 tests failed (the PR updated its own #5966 harness but missed this one — same class as prior harness-gap CI-reds). Added the extractFunc line; confirmed it was a harness gap, not a timestamp regression — the #5700 timestamp lives on the row header (rendered even when detail is deferred), so all 20 assertions pass unchanged, and the helper self-guards its own deps.

The fix — traced correct, reuses proven #5860 machinery

A. Row-detail deferral: a settled, collapsed transparent tool row renders header-only; _materializeTransparentToolDetail(row) builds the .tool-card-detail on first expand — idempotent (clears the deferred flag), recovering the tool call from _deferredToolCall or, after an innerHTML cache round-trip, from data-anchor-row-id → S.messages (the #5839 recovery pattern). The detail transplants buildToolCard's own output with the same anchor-suppressed post-processing → an expanded row is byte-identical to the eager path. Live/already-open rows unchanged. ✓

B. Per-turn cap: _TRANSPARENT_SETTLED_ROW_CAP=30 + _SLACK=10 → a turn with >40 rows renders only the last 30 behind a "Show N earlier steps" pill that materializes the prefix with viewport compensation; exemptions for the just-settled turn (keep-open token) and any turn revealed this session; the true Trace tool-count is stashed so "Trace: N tools" stays honest; "Expand all" reveals capped rows first; cache-restore re-wires the affordance. ✓

No XSS: the only interpolating innerHTML (the pill label, line 375) is esc()'d; everything else is static tab/chevron markup or buildToolCard's (hardened) output. ✓

Edge-case matrix

Scenario	Behavior
Settled collapsed tool row	header-only; detail built on first expand ✅
Expand a deferred row	byte-identical to eager (buildToolCard transplant) ✅
After innerHTML cache restore	recovers via data-anchor-row-id → S.messages (#5839) ✅
Turn ≤40 rows	never capped ✅ (boundary-tested: 40 uncapped / 41 capped)
Turn >40 rows	last 30 + "Show N earlier" pill, position held ✅
Just-settled turn / already-revealed	exempt from cap ✅
Trace label while capped	honest "N tools" (stashed count) ✅

Tests

• tests/test_issue5966_transparent_stream_lazy_dom.py — 22/22 (source-assertions for both parts + cache-recovery/count/expand-all/rehydrate wiring + a node-vm cap-arithmetic harness: 400→30 mounted, 12-row turn never capped, slack boundary 40/41). RED-on-master verified (21 fail on master).
• #5700 timestamp suite — 20/20 after the harness fix; 197 locale tests green.
• node --check clean. Full suite: 12687 passed / 0 failed in 421s (deselected the known darwin CRLF flake). CI green (18/18).
• The PR's real-browser measurement: 12,494 → 639 transcript DOM nodes (−94.9%) on a 400-tool turn, Trace label honest, position held on reveal.

Recommendation

✅ Approved after fixes. Parked at approval — ready for the release agent's merge/tag pipeline.

The load-bearing browser-DOM half of the Transparent-Stream freeze, faithfully reusing the #5860/#5839 deferral + #5839 cache-recovery machinery (byte-identical expanded rows, XSS-clean, honest Trace count, viewport-held reveal). The two CI-reds were a locale-parity miss and a pre-existing test-harness gap (not a behavioral regression — verified) — both fixed. Mutation-proven tests RED on master; full suite clean. Ship.

[nesquena-hermes]

Shipped in exp-v0.52.50 (closes #5966). Transparent Stream now defers settled tool-detail DOM + caps per-turn rows — the 28GB freeze is fixed. Full gate: nesquena independent review APPROVED (−94.9% DOM), Codex SAFE, stream-regression-gate GREEN all modes, Fable UX/arch SHIP (orphan-pill-on-collapse fix applied), CI 18/18. Thanks @curtisszmania-cytocync for the detailed report.