fix(chat): suppress browser overflow-anchor during JS scroll-anchor realign (mobile scroll jump-back)

[allenliang2022]

Problem

On phones, a reader watching a message would sometimes be yanked to an unrelated earlier turn without touching the screen — the recurring mobile scroll jump-back reports. It never reproduced on desktop, even with a mobile viewport in Playwright, which is what made it so hard to pin down.

Root cause

The .messages scroll container's resting overflow-anchor differs by device:

.messages { … overflow-anchor: auto; }                     /* touch devices */
@media (hover:hover) and (pointer:fine){ .messages{ overflow-anchor: none; } }  /* desktop only */

So on a phone the browser's native scroll-anchoring is active (auto), while on a hover+fine-pointer desktop it is off (none).

When _restoreMessageViewportAnchor writes scrollTop to realign the reader's anchor row and content height above the viewport changed in that same frame (a background render — worklog/tool/activity update, session-updated swap, etc.), the mobile browser's own scroll-anchoring also adjusts scrollTop. The two compensations stack, and the reader is thrown to a different turn. Desktop never has the browser layer, which is exactly why every desktop repro failed while phones kept jumping.

Measured on an isolated instance (mobile viewport): inserting 800px of above-viewport content compensates scrollTop by +800 in auto mode and 0 in none mode — a clean, quantified demonstration of the double-compensation.

Fix

_suppressBrowserOverflowAnchor(container) temporarily sets overflow-anchor: none around the JS scrollTop write in _restoreMessageViewportAnchor, then restores the prior value on the next frame after layout settles. It engages only when the computed value is auto (mobile) and is a pure no-op on desktop (already none, returns null). This removes the browser layer for exactly the one frame the JS is doing its own compensation, so the two can't stack.

The existing _fixMobileScrollJank() already does this for the innerHTML='' DOM-wipe path, but only there — it does not cover incremental background renders / anchor-realign, which is the gap this closes.

Verification

Isolated debug instance, mobile-viewport Playwright:

• mobile auto: above-viewport growth compensation 800 → 0 (browser layer suppressed during the JS write)
• desktop none: helper returns null, inline value untouched — byte-identical behavior
• streaming: real turn, mid-read follow, 0 jumps, content held
• regression suite: scroll/anchor/jump/mobile/unpin tests green (629 passed locally; the single local failure is a Windows-only WinError 206 command-line-too-long in test_anchor_fallback_ownership's Node harness — unrelated to this change, passes on Linux CI, which is green here)

Release note wording (per CONTRIBUTING — CHANGELOG left to the release workflow)

A reader on a phone is no longer yanked to an unrelated earlier turn when a background render shifts content above the viewport. On touch devices .messages rests at overflow-anchor: auto, so the browser's native scroll-anchoring double-compensated alongside the JS scrollTop realign in _restoreMessageViewportAnchor. The realign write now suppresses the browser's overflow-anchor for that one frame and restores it next frame (_suppressBrowserOverflowAnchor); it engages only when the resting value is auto (mobile) and is a pure no-op on desktop (already none). Streaming follow, desktop behavior, and the scroll-regression suite are unaffected.

Notes

• Mobile-only behavioral change; desktop is provably unaffected (no-op path).
• Complements the earlier settle/scroll fixes (fix(webui): keep a following reader pinned through streaming growth and SSE recovery #5217, fix(webui): render a server-initiated turn that finished during an SSE gap on a visible tab #5248, fix(chat): preserve manual live worklog scroll #5253, fix(chat): keep just-settled worklog open for unpinned readers too (mobile scroll jump-back) #5260) — this addresses the distinct browser-vs-JS double-compensation class that those didn't cover.

[greptile-apps]

Greptile Summary

This PR fixes a mobile-only scroll jump-back (往回大跳) where the browser's native overflow-anchor: auto scroll-compensation and the JS scrollTop write in _restoreMessageViewportAnchor both fired in the same frame, doubling the scroll adjustment and yanking the reader to an unrelated turn. Desktop was unaffected because the CSS media query already pins .messages to overflow-anchor: none there.

• Adds _browserOverflowAnchorActive (computed-style predicate) and _suppressBrowserOverflowAnchor (scoped inline override + rAF-deferred restore), then threads suppression into _restoreMessageViewportAnchor and a new _postProcessWithAnchorSuppression wrapper that also covers the async post-render settle window (syntax highlighting, KaTeX, Mermaid, etc.).
• Refactors _fixMobileScrollJank to route through the same _browserOverflowAnchorActive predicate so the two guards cannot drift if the CSS media query changes.
• Updates five test files that asserted on the old literal requestAnimationFrame(()=>postProcessRenderedMessages(inner)) to assert on the new wrapper instead, preserving behavioral coverage.

Confidence Score: 5/5

Safe to merge. The change is mobile-only and the desktop path is a verified no-op via the computed-style predicate returning false.

The suppression logic is well-scoped: it engages only when getComputedStyle(el).overflowAnchor === 'auto' (mobile), restores via a rAF-deferred callback with an ownership guard, and the released boolean prevents double-restore. The refactor of _fixMobileScrollJank to use the shared predicate is correct and eliminates a potential drift between two guards. The _postProcessWithAnchorSuppression wrapper correctly re-acquires suppression in the post-render frame and holds it for one extra frame to cover late image-decode/KaTeX/Mermaid reflow. All updated tests match the implementation.

No files require special attention.

Important Files Changed

Filename	Overview
static/ui.js	Core fix: adds _browserOverflowAnchorActive, _suppressBrowserOverflowAnchor, and _postProcessWithAnchorSuppression; threads suppression into _restoreMessageViewportAnchor; refactors _fixMobileScrollJank to use the shared predicate. Logic is sound and desktop paths are verified no-ops.
tests/test_issue4856_android_scroll_regression.py	Adds test_post_process_runs_under_overflow_anchor_suppression covering the new wrapper's existence, its call to the shared suppressor, the extra-frame rAF deferral, and the absence of any raw rAF dispatch to postProcessRenderedMessages. All assertions match the implementation.
tests/test_csv_table_rendering.py	Updated literal rAF-assertion to match new _postProcessWithAnchorSuppression dispatch; added wrapper-chain assertion to guard against future renames orphaning the test.
tests/test_anchor_fallback_ownership.py	Adds _postProcessWithAnchorSuppression stub to the renderMessages mock harness so the test suite recognises the new function without treating it as undefined.
tests/test_pdf_html_preview.py	Count-based dispatch assertion updated to match the new wrapper name; chain assertion added.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant R as renderMessages()
    participant FMJ as _fixMobileScrollJank()
    participant RMVA as _restoreMessageViewportAnchor()
    participant SBA as _suppressBrowserOverflowAnchor()
    participant PPAS as _postProcessWithAnchorSuppression()
    participant PPR as postProcessRenderedMessages()
    participant B as Browser anchor engine

    Note over R: Frame N (sync render)
    R->>FMJ: call (before DOM wipe)
    FMJ->>SBA: _browserOverflowAnchorActive(el)?
    SBA-->>FMJ: true (mobile) / false (desktop→return)
    FMJ->>B: "inline overflow-anchor = 'none'"
    FMJ-->>R: schedules rAF to restore ''

    R->>RMVA: _restoreMessageViewportAnchor(anchor, 0)
    RMVA->>SBA: _suppressBrowserOverflowAnchor(container)
    SBA->>B: "inline overflow-anchor = 'none'"
    SBA-->>RMVA: release fn
    RMVA->>B: "container.scrollTop += delta"
    Note over B: browser layer suppressed — no double-compensation
    RMVA->>RMVA: release() → schedules rAF(restore) for N+1

    R->>PPAS: requestAnimationFrame(_postProcessWithAnchorSuppression)

    Note over B: Frame N+1 — rAF restore fires, then PPAS
    B-->>B: "restore overflow-anchor = '' (CSS auto resumes)"

    PPAS->>SBA: _suppressBrowserOverflowAnchor(scroller)
    SBA->>B: "inline overflow-anchor = 'none' (re-suppressed)"
    SBA-->>PPAS: release fn
    PPAS->>PPR: postProcessRenderedMessages(container)
    Note over PPR: highlightCode, katex, mermaid,<br/>csv/diff/pdf/excalidraw hydration
    Note over B: height changes — browser layer suppressed
    PPAS->>PPAS: finally: requestAnimationFrame(release) for N+2

    Note over B: Frame N+2 — release fires
    PPAS->>PPAS: release() → schedules rAF(restore) for N+3

    Note over B: Frame N+3 — restore fires
    B-->>B: "restore overflow-anchor = '' (CSS auto resumes on mobile)"

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
    participant R as renderMessages()
    participant FMJ as _fixMobileScrollJank()
    participant RMVA as _restoreMessageViewportAnchor()
    participant SBA as _suppressBrowserOverflowAnchor()
    participant PPAS as _postProcessWithAnchorSuppression()
    participant PPR as postProcessRenderedMessages()
    participant B as Browser anchor engine

    Note over R: Frame N (sync render)
    R->>FMJ: call (before DOM wipe)
    FMJ->>SBA: _browserOverflowAnchorActive(el)?
    SBA-->>FMJ: true (mobile) / false (desktop→return)
    FMJ->>B: "inline overflow-anchor = 'none'"
    FMJ-->>R: schedules rAF to restore ''

    R->>RMVA: _restoreMessageViewportAnchor(anchor, 0)
    RMVA->>SBA: _suppressBrowserOverflowAnchor(container)
    SBA->>B: "inline overflow-anchor = 'none'"
    SBA-->>RMVA: release fn
    RMVA->>B: "container.scrollTop += delta"
    Note over B: browser layer suppressed — no double-compensation
    RMVA->>RMVA: release() → schedules rAF(restore) for N+1

    R->>PPAS: requestAnimationFrame(_postProcessWithAnchorSuppression)

    Note over B: Frame N+1 — rAF restore fires, then PPAS
    B-->>B: "restore overflow-anchor = '' (CSS auto resumes)"

    PPAS->>SBA: _suppressBrowserOverflowAnchor(scroller)
    SBA->>B: "inline overflow-anchor = 'none' (re-suppressed)"
    SBA-->>PPAS: release fn
    PPAS->>PPR: postProcessRenderedMessages(container)
    Note over PPR: highlightCode, katex, mermaid,<br/>csv/diff/pdf/excalidraw hydration
    Note over B: height changes — browser layer suppressed
    PPAS->>PPAS: finally: requestAnimationFrame(release) for N+2

    Note over B: Frame N+2 — release fires
    PPAS->>PPAS: release() → schedules rAF(restore) for N+3

    Note over B: Frame N+3 — restore fires
    B-->>B: "restore overflow-anchor = '' (CSS auto resumes on mobile)"

Loading

_{Reviews (7): Last reviewed commit: "test(chat): stub _postProcessWithAnchorS..." | Re-trigger Greptile}

[greptile-apps]

CHANGELOG touched directly by a contributor PR

Per this repo's stated policy, CHANGELOG.md is maintained exclusively by the release process via release: vX.Y.Z commits authored by the release agent — individual contributor PRs never touch CHANGELOG.md directly. Adding this entry now could cause a merge conflict or duplicate entry when the release agent writes its own block on top of the [Unreleased] section.

Rule Used: Do not flag missing CHANGELOG.md updates on indivi... (source)

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[allenliang2022]

Thanks for the review. Addressed the CHANGELOG policy note: reverted the direct CHANGELOG.md edit (force-pushed d7b5cac3, now static/ui.js only) and moved the release-note wording into the PR body per CONTRIBUTING. The behavioral analysis in the summary matches the intent exactly — desktop is a verified no-op, suppression is scoped to the single JS-compensation frame.

[nesquena-hermes]

Independent verification of the load-bearing claim, plus one consistency note.

The CSS asymmetry checks out

The whole fix rests on .messages resting at overflow-anchor: auto on touch and none only on hover+fine-pointer desktops. Confirmed on origin/master at static/style.css:2223-2224:

.messages{ … overscroll-behavior-y:contain; overflow-anchor:auto; }
@media (hover:hover) and (pointer:fine){ .messages{ overflow-anchor:none; } }

So the browser's native scroll-anchoring is live on mobile and off on desktop, which is exactly why the JS scrollTop realign in _restoreMessageViewportAnchor double-compensated on phones only. The computed !== 'auto' early-return in the new helper makes desktop a true no-op against that resting none.

The gap this closes is real

_fixMobileScrollJank (static/ui.js:12184) already suppresses overflow-anchor for the innerHTML='' wipe path, but the anchor-realign write in _restoreMessageViewportAnchor was unguarded. That function is on the incremental streaming path: _restoreMessageScrollSnapshotSameFrame calls it at ui.js:12141 and 12145 for same-frame tool/worklog/activity renders. Those are precisely the "content height above viewport changed" events described, so wiring the suppression here is the right seam.

Two things I checked that make me comfortable

1. No leaked suppression on the false path. _restoreMessageViewportAnchor has several early return false exits (if(!row&&anchorKey) return false;) that all fire before the new _suppressBrowserOverflowAnchor(container) call. So when the direct call at ui.js:12141 returns false and the remount path retries at 12145, the first call never suppressed anything to leak. The re-entrant second call sees inline none already set → computed resolves none → returns null → no double-schedule. Benign.

2. No extra forced reflow. The getComputedStyle(...).overflowAnchor read lands after the two getBoundingClientRect() calls, so layout is already clean at that point and the style read is cheap. It doesn't add a second reflow to the hot render path.

One small consistency note (non-blocking)

The new helper gates on getComputedStyle(container).overflowAnchor === 'auto', while the older _fixMobileScrollJank gates on window.matchMedia('(hover:hover) and (pointer:fine)').matches. The computed-value approach here is actually the more robust of the two (it reflects the real resting value including any inline override), but the two guards can now diverge if the CSS media query ever changes. Not a blocker for this PR, just flagging that a future cleanup could route both through one shared "is the browser anchor layer active?" check so they can't drift apart.

CI is green across the matrix and the change is additive (+42 lines, static/ui.js only). Root cause, fix location, and no-op desktop path all verified.

[allenliang2022]

Thanks for the thorough independent verification — and good call on the consistency note. I went ahead and unified the two guards in 9b61b97b: extracted a single _browserOverflowAnchorActive(el) predicate (the computed-value test, since as you noted it's the more robust of the two) and routed BOTH _suppressBrowserOverflowAnchor and _fixMobileScrollJank through it, so the mobile-vs-desktop gate lives in exactly one place and the two can't drift if the CSS media query ever changes.

Verified on an isolated debug instance (worktree bytes): the predicate returns true for auto/false for none; the suppress helper still engages + restores on auto and no-ops (returns null) on none; and _fixMobileScrollJank still suppresses correctly on auto via the shared predicate. Still static/ui.js only, CI matrix green.

[allenliang2022]

Pushed a follow-up commit 7536f6f1 that closes a second path of the same double-compensation bug — the async post-render settle window.

What was still leaking: the synchronous guards (_fixMobileScrollJank / _suppressBrowserOverflowAnchor) only cover the render frame itself. But postProcessRenderedMessages() (syntax highlight, inline diff/csv/pdf/html/excalidraw hydration, katex/mermaid) is scheduled a frame later via requestAnimationFrame(), after those guards have released. Each of those operations can change the height of rows above the viewport, and on mobile (overflow-anchor:auto) the browser's native anchor engine then compensates scrollTop a second time in that unguarded frame — yanking an unpinned reader to another turn. This is the residual mobile jump-back that survived the first fix.

The fix: wrap all three deferred post-process dispatches (fast-path cache branch, main render tail, live-tool remount) in a small _postProcessWithAnchorSuppression() that routes through the same shared _suppressBrowserOverflowAnchor() and holds suppression one extra frame so late media/layout reflow is covered too. Desktop rests at overflow-anchor:none, so the wrapper is a verified no-op there.

Reproduced + verified on an isolated debug instance with a cloned 1179-message session:

above-viewport +350px during async settle	scrollTop delta
mobile auto, before fix	+350 (jump)
mobile auto, with wrapper	0
desktop none, with wrapper	0 (no-op)

Added a regression test (test_post_process_runs_under_overflow_anchor_suppression) that is base-fails/head-passes: it asserts the wrapper exists, routes through the shared suppress helper, defers release one frame, and that no raw requestAnimationFrame(()=>postProcessRenderedMessages(...)) dispatch remains. Still static/ui.js (+ the test). 45 related scroll-regression tests green locally.

[nesquena-hermes]

🔬 Gate certification — RED ⛔ (red CI: a behavior-preserving refactor orphaned 6 sibling source-string tests) + visible → Nathan screenshot

Certified head: sha:7536f6f1 (rebased onto current master, git apply clean) · PR: #5338 · allenliang2022, fix(chat): suppress browser overflow-anchor during JS scroll-anchor realign (mobile scroll jump-back)
Verdict: The core fix is sound (wraps the post-render pass in overflow-anchor suppression so late media/katex/mermaid reflow can't re-anchor and cause the mobile scroll jump-back). But CI is RED because the refactor renamed the post-render call site and 6 pre-existing sibling tests string-match the old literal — they need updating. Behavior is preserved (verified). Fix the 6 tests, then it's a visible mobile-scroll fix that needs Nathan's screenshot sign-off.

What I ran (rebased worktree /tmp/wt-rebase-5338)

Gate	Result
Rebase onto current master	✅ git apply clean; ui.js + new test
CI (live)	❌ 12 shard jobs fail — I fetched the raw logs: test_csv_loadCsvInline_called_after_render, test_excalidraw_called_after_render, test_loadDiffInline_called_in_post_render, test_anchor_fallback_ownership, …
Root-cause (mine)	orphaned source-string tests, NOT a behavior break (below)

Findings

Root cause — behavior-preserving refactor orphaned 6 source-string tests (the red CI): the PR replaced the post-render call requestAnimationFrame(()=>postProcessRenderedMessages(inner)) with requestAnimationFrame(()=>_postProcessWithAnchorSuppression(restored)) (ui.js:7910). I verified the new wrapper _postProcessWithAnchorSuppression(container) still calls postProcessRenderedMessages(container) inside a try/finally (just holds overflow-anchor suppression across one more frame). So CSV/Excalidraw/diff/JSON/PDF inline loading all still run — behavior is intact. But 6 pre-existing tests assert the old literal string and now fail:

• tests/test_csv_table_rendering.py, tests/test_excalidraw_inline_embed.py, tests/test_issue483_inline_diff_viewer.py, tests/test_issue484_json_tree_viewer.py, tests/test_issue347.py, tests/test_pdf_html_preview.py (+ the anchor-ownership test).
• Fix: update those 6 tests to assert the new consolidated call (_postProcessWithAnchorSuppression scheduled via requestAnimationFrame, which itself calls postProcessRenderedMessages) — or, better, assert the behavior (postProcessRenderedMessages is invoked post-render) rather than the exact rAF literal, so a future wrapper rename doesn't re-break them. The PR added its own test_issue4856_android_scroll_regression.py but must also fix the 6 siblings its refactor touched.

The fix concept itself looks sound (pending green + screenshot): _suppressBrowserOverflowAnchor(scroller) sets overflow-anchor:none during the JS scroll-anchor realign, held across the post-render frame, then rAF-deferred restore — a reasonable approach to the Android/mobile scroll jump-back (#4856). I did not deep-gate the scroll behavior yet since CI is red; re-gate after the tests are fixed.

Recommendation to the next agent

RED — gate-fail/changes-requested: update the 6 orphaned source-string tests to match the _postProcessWithAnchorSuppression refactor (behavior is preserved — postProcessRenderedMessages still runs, so this is a test-fix not a code-fix). Prefer behavior-assertions over rAF-literal string matches to prevent re-breakage. Once green, this is a VISIBLE mobile-scroll fix → Nathan screenshot sign-off (the dossier flags NATHAN VISUAL SIGN-OFF; nesquena-hermes already posted a positive independent-verification comment). Then I'll deep-gate the scroll behavior (live mobile-viewport drive of the jump-back scenario). concept 4/5 (real Android scroll-jump-back fix, #4856). Author @allenliang2022 (T2). crit=3.

---

Gate-certifier layer (warm-up → gate → release). I do not merge/tag/deploy. Rebased onto current master; CI-red root-caused to 6 orphaned source-string tests (fetched raw CI logs first), refactor verified behavior-preserving (wrapper still calls postProcessRenderedMessages). Cert valid for sha:7536f6f1.

[allenliang2022]

Thanks for the RED gate-cert and the precise root-cause — you were exactly right. Fixed in 4027c2f7.

What I did (test-fix, not code-fix — behavior is preserved): updated the 6 orphaned source-string tests to assert the behavior chain rather than the old rAF literal, per your recommendation:

• test_csv_table_rendering, test_excalidraw_inline_embed, test_issue483_inline_diff_viewer, test_issue484_json_tree_viewer, test_issue347 (the katex-wiring test), test_pdf_html_preview.
• Each now asserts (a) post-render is scheduled via requestAnimationFrame(()=>_postProcessWithAnchorSuppression(...)), and (b) the _postProcessWithAnchorSuppression wrapper still invokes postProcessRenderedMessages(container). So a future wrapper rename can't re-orphan them, and the real behavior (CSV/Excalidraw/diff/JSON/PDF/katex/mermaid inline loading still runs post-render) is what's pinned.
• test_pdf_html_preview's count assertion was kept as == 2 but retargeted to the wrapper's (inner) dispatches (the (restored) dispatch was never in that count).

Verified locally: the 6 updated assertions pass (148 passed in the affected suite). The only local failures are the pre-existing Windows-only WinError 206 command-line-too-long in the Node-harness tests (test_issue347 latex-delimiter cases, test_anchor_fallback_ownership) — I confirmed those fail identically with my change stashed, so they're unrelated environment artifacts, green on Linux CI.

test_anchor_fallback_ownership itself stubs its own postProcessRenderedMessages, so it wasn't orphaned by the rename (its 10 non-harness assertions pass). CI should now be green across the matrix.

[nesquena-hermes]

🔬 Gate certification — RED ⛔ (converged 6/7: one behavioral test's harness still needs the new helper) — CI red on 1 test

Certified head: sha:4027c2f7 (rebased onto current master, git apply clean) · PR: #5338 · allenliang2022, fix(chat): suppress browser overflow-anchor during JS scroll-anchor realign (mobile scroll jump-back)
Verdict: Almost there — the re-push fixed the 6 orphaned source-string tests I flagged (all pass now), but one 7th test still fails: test_anchor_fallback_ownership executes an extracted slice of renderMessages and hits ReferenceError: _postProcessWithAnchorSuppression is not defined because its Node harness doesn't extract/stub the new helper. One more targeted test fix, then green → screenshot-gate.

What I ran (rebased worktree /tmp/wt-rebase-5338b)

Gate	Result
Rebase onto current master	✅ git apply clean
CI (live)	❌ shard 2 (all 3 Pythons) fail — I fetched raw logs: only test_anchor_fallback_ownership
The 6 previously-orphaned tests	✅ 151/151 pass (contributor applied my fix-spec)
Root-cause of the remaining failure (mine)	test-harness gap, not a behavior break (below)

Findings

✅ CONVERGED 6/7 — the source-string tests are fixed: the re-push (commit "test(chat): update 6 post-render tests orphaned by the _postProcessWithAnchorSuppression [refactor]") updated test_csv_table_rendering, test_excalidraw_inline_embed, test_issue483_inline_diff_viewer, test_issue484_json_tree_viewer, test_issue347, test_pdf_html_preview — all 151 pass now.

⛔ CI-RED — the 7th test's Node harness lacks the new helper (tests/test_anchor_fallback_ownership.py:62): this test doesn't string-match — it executes renderMessages in Node by extracting it via _function_source() (plus _transparentStreamOrderedParts, _legacySettledFallbackHasToolMetadata) and evals with fake-DOM stubs. The PR's renderMessages now schedules requestAnimationFrame(()=>_postProcessWithAnchorSuppression(restored)), but the harness doesn't extract or stub _postProcessWithAnchorSuppression, so the rAF callback throws ReferenceError: _postProcessWithAnchorSuppression is not defined. In real ui.js it's a hoisted function (defined at ui.js:15027) so production is fine — this is purely a test-harness gap the refactor introduced.

• Fix (one of): in test_anchor_fallback_ownership, either (a) also extract _postProcessWithAnchorSuppression (+ its dep _suppressBrowserOverflowAnchor) into the eval'd script, or (b) stub _postProcessWithAnchorSuppression as a no-op in the harness (this test is about anchor-ownership during legacy-activity rebuilds, not the post-render pass, so a no-op stub is legitimate). Prefer a stub — the test shouldn't depend on the post-render internals.

The fix concept remains sound (deferred to post-green): overflow-anchor suppression held across the post-render frame to stop the Android/mobile scroll jump-back (#4856); nesquena-hermes posted a positive independent-verification comment.

Recommendation to the next agent

RED — gate-fail/changes-requested: one remaining test fix — make test_anchor_fallback_ownership's Node harness provide _postProcessWithAnchorSuppression (stub as no-op, or extract it + _suppressBrowserOverflowAnchor). The 6 source-string tests are already fixed (151/151). Behavior is intact (production hoists the function fine); this is the last test-harness gap. Once green, this VISIBLE mobile-scroll fix needs Nathan screenshot sign-off (then I'll live-drive the jump-back scenario on a mobile viewport). concept 4/5 (#4856 Android scroll-jump-back). Author @allenliang2022 (T2). crit=3.

---

Gate-certifier layer (warm-up → gate → release). I do not merge/tag/deploy. Rebased onto current master; 6/7 orphaned tests now pass (151/151), the 7th root-caused to a Node-harness missing the hoisted _postProcessWithAnchorSuppression (ReferenceError, not a behavior break). Cert valid for sha:4027c2f7.

[nesquena-hermes]

🔬 Gate certification — GREEN (engineering) ✅ · CONVERGED · ⏸️ visible → Nathan screenshot sign-off

Certified head: sha:bf2bb0ce (clean rebase, branch gate-rebase/5338-overflow-anchor) · PR: #5338 · allenliang2022, fix(chat): suppress browser overflow-anchor during JS scroll-anchor realign (mobile scroll jump-back)
Verdict: Engineering GREEN after 3 gate rounds — all 7 orphaned tests fixed, suite green, Codex SAFE, and I verified the suppression is temporary/restored (no overflow-anchor:none leak) with behavior intact. This is a visible mobile-scroll fix, so it now needs Nathan's screenshot/motion sign-off before merge (the fix targets a motion artifact — the Android scroll jump-back, #4856).

What I ran (rebased worktree /tmp/wt-rebase-5338c)

Gate	Result
Rebase onto current master	✅ git apply clean
Codex (reproduce)	SAFE TO SHIP — gated the rebased worktree, 0 findings
Full pytest suite	11515 passed, 0 failed (all 7 orphaned tests now pass)
Suppression-mechanism read (mine)	✅ temporary + restored, no leak (below)

Findings

✅ CONVERGED over 3 rounds — CI is green: round 1 flagged 6 orphaned source-string tests (the refactor renamed the post-render call); round 2 the contributor fixed those 6 (151/151) but a 7th behavioral test (test_anchor_fallback_ownership) hit a runtime ReferenceError (its Node harness eval'd renderMessages without the new helper); round 3 (this) the contributor added a no-op stub function _postProcessWithAnchorSuppression() {} in that harness — a legitimate stub (the test verifies anchor-ownership in legacy-activity rebuilds, not the post-render pass). All 7 pass; suite 11515/0.

✅ Behavior intact + no suppression leak: _postProcessWithAnchorSuppression(container) still calls postProcessRenderedMessages(container) (CSV/Excalidraw/diff/JSON/PDF post-render all run). _suppressBrowserOverflowAnchor(container) only engages when the browser anchor is active (skips desktop), saves the prior inline overflow-anchor, sets none, and returns a _release() that rAF-defers a restore to the saved value — guarded (only restores if it still owns the suppression, idempotent via a released flag). So suppression is scoped to the realign + one frame, then restored — no permanent overflow-anchor:none leak and no clobbering a concurrent render.

⏸️ Visible surface → Nathan sign-off: the fix targets the Android/mobile scroll jump-back (#4856) — a motion artifact a static screenshot can't capture. Next step: live-drive the jump-back scenario on a mobile viewport (scroll up in a long conversation while a new turn streams + media reflows) before/after, and get Nathan's approval. nesquena-hermes already posted a positive independent-verification comment.

Recommendation to the next agent

Engineering-GREEN — merge from branch gate-rebase/5338-overflow-anchor (sha:bf2bb0ce), NOT the PR's stale head 2c6ad82b — AFTER Nathan's visible sign-off. Converged cleanly over 3 rounds; Codex SAFE + suite 11515/0 + suppression verified temporary/no-leak + behavior intact. Because it's a visible mobile-scroll fix, it's not an autonomous merge: live-drive + screenshot/GIF the jump-back before/after for Nathan. concept 4/5 (real #4856 Android fix; nesquena-hermes independently verified). Credit @allenliang2022 (co-authored). crit=3.

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Gate-certifier layer (warm-up → gate → release). I do not merge/tag/deploy. Rebased onto current master; all 7 orphaned tests fixed (suite 11515/0), suppression verified temporary/restored (no leak), behavior intact, Codex SAFE. Engineering green; visible mobile-scroll fix → Nathan screenshot sign-off. Cert valid for sha:bf2bb0ce.

[nesquena-hermes]

Shipped in v0.51.797. Thanks @allenliang2022 — routing both guards through the single _browserOverflowAnchorActive computed-value predicate (desktop no-op, mobile-only suppression with rAF restore) is a clean, drift-proof fix. Codex SAFE, full suite green.