fix(web): numbered composer lists nest and lift correctly#17138

Problem

Typing 1. first, Shift+Enter, Tab, and nested in either web composer mode kept the outer item number and inserted only two spaces. The sent Markdown rendered as a flat list. Shift+Enter on an empty nested item in the plain composer also left the list instead of lifting one level.

Change

Tab aligns children with their parent's Markdown content column and starts or continues the child numbering while preserving the caret. Empty nested items lift one level before leaving the list. The backward scan respects multiline mention chips and tab-separated markers.

Reuses #17138, preserving @michal-billtech's commits and adapting the fix to current main's caret and renumbering helpers.

Scope and approval

Fixes https://github.com/pingdotgg/t3code/issues/17124

Triaged bug via the automated issue flow. The change is confined to the shared web/desktop composer helper and its focused regressions. Shift+Tab retains its existing shortcut.

Verification

CI follow-up registers the browser-injected fixture in the existing Knip entry list. Scoped lint/format, Knip files/dependencies and web exports checks, and 24 composer-helper tests pass. This configuration-only commit leaves the captured runtime bytes unchanged.

• Regression tests fail before the fix for ordered nesting, empty-item lifting, tab-separated parents, and multiline mention-chip boundaries.
• 288 related composer tests passed after implementation; an independent reviewer passed 395 tests across eight related files.
• Targeted lint and formatting passed; web typecheck passed.
• Real Linux web client reproduced the flat sent message on main, then verified content-column indentation, child numbering, and caret behavior after the fix in both composer modes.

Full evidence report · Fixture matrix

Evidence

Issue: #17124. Recording correction completed within its fresh 30-minute budget. No public PR/issue write, push, label, or merge was performed.

Before production: 044f07257c. After implementation: 53ba38bb47. Earlier fixture-only head: 03613cb5d8 (fixture-only commit). Production code is byte-identical to the After implementation. The replacement Before captures temporarily replaced only the helper at the fixed integrated head. All other web production files match Before; the web test file also differs. Backend files remain those of the integrated head. Helper restored and worktree clean.

Final integrated head: ae038086a6, merging current main 22840ab943. Main added no web changes; captured production composer bytes remain identical.

Coverage and environment

16/16 replacement recordings; 80/80 A–E matrix cells checked in actual encoded frames, including 208/208 X demonstrations and 176/176 seed states. Rich/plain × 1440×900/390×844 CSS px × light/dark × Before/After. No missing matrix rows. D prefix offset is plain-only; rich uses its reachable start-of-content caret, as planned. All canonical starting texts matched the requested text; rich prefix caret position normalized structurally. Original still-capture per-operation text and caret observations: observations.json. Pixel counts and image dimensions: metrics.json.

Retained isolated server: localhost:6215, backend 14255, home /home/ubuntu/wt/issue-17124/.t3. No servers started/stopped. Own T3 preview tab, paired through pair --base-dir against this home; no tokenized capture URLs. Chrome 154 on Linux x86_64, zoom 1, DPR 2, default system font (-apple-system/BlinkMacSystemFont/Segoe UI/system-ui/sans-serif), fonts ready before capture. Recordings retain the whole surface at 2880×1800 and 780×1688 physical px. The preview screenshot transport downscales desktop PNGs to 1280×800; mobile PNGs remain 780×1688. Matching stills/diffs use these exact returned dimensions. Browser timestamp formatter fixed to 12:00 UTC; server clock unchanged.

Each final sequence starts from a fresh identical empty synthetic thread fixture (different durable IDs, recorded in observations) rather than reusing one ID after sending. This is a deviation from literal same-thread-ID reuse; it keeps history, title, project, checkout, and fixtures identical at sequence start. Sidebars collapsed/offscreen. Earlier draft-only, expanded-sidebar, and incorrect-theme attempts were superseded and excluded from upload.

Chapter A dispatches the canonical current draft with defer_start, then interrupts with holdQueue=true. This uses real guarded app commands and the real message renderer, but bypasses the Submit button to avoid a real provider. Persisted projections for all 16 final threads confirm interrupted status, startedAt=null, and zero providerTurns. Before message DOM is one ordered list with two sibling items; After has an ordered list nested inside the parent item. The renderer displays the nested marker as a. while canonical Markdown retains 1. This proves the fixture dispatch/render path, not provider execution or the ordinary Submit-button path.

Observed differences

• A: Before adds two spaces and keeps 2./11.; After aligns children at three/four columns and resets to 1. Typing X stays mid-word. The sent fixture becomes truly nested in After, versus flat siblings in Before.
• B: After uses three spaces and child 2. after the sibling/grandchild scan; Before uses two spaces and original 3. Existing descendant lines remain unchanged.
• C: Plain After lifts through child 2., top-level 2., then exits; Before removes the nested marker immediately and subsequent newlines remain blank. Rich behavior is parity: both lift one level each time. X and deletion of only X demonstrate each caret.
• D: No-parent and blank-line fallback are unchanged at two spaces. Plain prefix caret changes from two spaces + X11. to four spaces + X1.; rich content caret yields four spaces + 1. Xchild after normalization.
• E: Bullet/task indentation remains two spaces with original markers. Matching delimiter continues 09) to 10) at the existing child indent; mismatched delimiter starts 1. at that indent. Before keeps current 2)/2. and two spaces.
• Stills also contain the intentional fixture interruption status and the ordinary git/context controls. Caret blink, antialiasing, and transient rendering timing can contribute to the zero-threshold pixel mask; the masks are not a claim that every changed pixel is a regression. No seed conversation text is visible in the selected captures.

Paired recordings and stills

All 16 original recordings are superseded. Native preview cursor and click indicators can be visible in the replacement clips. Times below are approximate ranges inspected in the decoded replacement videos. They are not RPC wall-clock timestamps; the capture transport introduces a variable delay. Each seed and every keyboard result was held for at least 1.05 seconds; the final state was held for three additional seconds before its endpoint screenshot and recording stop. No audio narration is claimed; the written checkpoints describe the visible actions. Seed means reset with production buildDocJson/serializeEditorDoc and EditorView dispatch. Tab/X and Shift+Enter/X use actual preview keyboard events through ChatComposer. After each C observation, only X is deleted before the next Shift+Enter. Each sequence is A→B→C→D→E. The A-rendered and E endpoint stills each have two full-surface diff masks: max absolute RGB-channel delta >0 and >16 on the 0–255 scale. Changed pixels are amplified to solid magenta over a muted reference image; no crop, translation, registration, or ignored region.

rich · 1440×900 · light

Before chapters (decoded-video ranges): A 3–14s; B 14–18s; C 18–30s; D 30–42s; E 42–61s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 16–17s; C1 X visible 20–21s; C2 X visible 24–25s; C3 X visible 28–29s; D0 X visible 33–34s; D1 X visible 37–38s; D2 X visible 40–41s; E0 X visible 45–46s; E1 X visible 49–50s; E2 X visible 53–54s; E3 X visible 57–58s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–12s; B 12–15s; C 15–27s; D 27–38s; E 38–54s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 8–9s; B0 X visible 14–15s; C1 X visible 18–19s; C2 X visible 21–22s; C3 X visible 25–26s; D0 X visible 29–30s; D1 X visible 33–34s; D2 X visible 36–37s; E0 X visible 40–41s; E1 X visible 43–44s; E2 X visible 47–48s; E3 X visible 51–52s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 8,881 pixels; >16 = 3,966 pixels.

E composer endpoint

Amplified differences: >0 = 8,566 pixels; >16 = 3,706 pixels.

rich · 1440×900 · dark

Before chapters (decoded-video ranges): A 3–16s; B 16–20s; C 20–35s; D 35–47s; E 47–66s.

Before typing checkpoints: A0 X visible 6–7s; A1 X visible 10–11s; B0 X visible 18–19s; C1 X visible 23–24s; C2 X visible 28–29s; C3 X visible 32–33s; D0 X visible 37–38s; D1 X visible 42–43s; D2 X visible 46–47s; E0 X visible 50–51s; E1 X visible 53–54s; E2 X visible 57–58s; E3 X visible 62–63s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–12s; B 12–15s; C 15–27s; D 27–38s; E 38–55s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 8–9s; B0 X visible 14–15s; C1 X visible 18–19s; C2 X visible 21–22s; C3 X visible 25–26s; D0 X visible 30–31s; D1 X visible 34–35s; D2 X visible 37–38s; E0 X visible 41–42s; E1 X visible 44–45s; E2 X visible 48–49s; E3 X visible 52–53s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 8,796 pixels; >16 = 4,034 pixels.

E composer endpoint

Amplified differences: >0 = 8,481 pixels; >16 = 3,757 pixels.

rich · 390×844 · light

Before chapters (decoded-video ranges): A 3–14s; B 14–19s; C 19–33s; D 33–45s; E 45–64s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 10–11s; B0 X visible 17–18s; C1 X visible 22–23s; C2 X visible 26–27s; C3 X visible 30–31s; D0 X visible 36–37s; D1 X visible 40–41s; D2 X visible 43–44s; E0 X visible 48–49s; E1 X visible 52–53s; E2 X visible 56–57s; E3 X visible 60–61s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–13s; B 13–17s; C 17–30s; D 30–41s; E 41–59s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 15–16s; C1 X visible 19–20s; C2 X visible 23–24s; C3 X visible 27–28s; D0 X visible 32–33s; D1 X visible 36–37s; D2 X visible 40–41s; E0 X visible 44–45s; E1 X visible 48–49s; E2 X visible 51–52s; E3 X visible 56–57s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 26,552 pixels; >16 = 12,052 pixels.

E composer endpoint

Amplified differences: >0 = 25,381 pixels; >16 = 10,970 pixels.

rich · 390×844 · dark

Before chapters (decoded-video ranges): A 2–13s; B 13–17s; C 17–32s; D 32–44s; E 44–63s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 15–16s; C1 X visible 19–20s; C2 X visible 23–24s; C3 X visible 28–29s; D0 X visible 34–35s; D1 X visible 38–39s; D2 X visible 42–43s; E0 X visible 46–47s; E1 X visible 50–51s; E2 X visible 55–56s; E3 X visible 59–60s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–12s; B 12–16s; C 16–29s; D 29–41s; E 41–59s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 8–9s; B0 X visible 15–16s; C1 X visible 18–19s; C2 X visible 22–23s; C3 X visible 26–27s; D0 X visible 31–32s; D1 X visible 35–36s; D2 X visible 39–40s; E0 X visible 44–45s; E1 X visible 48–49s; E2 X visible 51–52s; E3 X visible 55–56s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 26,502 pixels; >16 = 12,010 pixels.

E composer endpoint

Amplified differences: >0 = 25,386 pixels; >16 = 10,996 pixels.

plain · 1440×900 · light

Before chapters (decoded-video ranges): A 3–15s; B 15–20s; C 20–33s; D 33–44s; E 44–64s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 10–11s; B0 X visible 18–19s; C1 X visible 22–23s; C2 X visible 26–27s; C3 X visible 30–31s; D0 X visible 35–36s; D1 X visible 39–40s; D2 X visible 43–44s; E0 X visible 47–48s; E1 X visible 51–52s; E2 X visible 55–56s; E3 X visible 60–61s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–12s; B 12–15s; C 15–27s; D 27–38s; E 38–55s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 8–9s; B0 X visible 14–15s; C1 X visible 18–19s; C2 X visible 21–22s; C3 X visible 25–26s; D0 X visible 29–30s; D1 X visible 33–34s; D2 X visible 36–37s; E0 X visible 40–41s; E1 X visible 44–45s; E2 X visible 47.0–47.75s; E3 X visible 51–52s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 8,550 pixels; >16 = 3,693 pixels.

E composer endpoint

Amplified differences: >0 = 8,937 pixels; >16 = 4,027 pixels.

plain · 1440×900 · dark

Before chapters (decoded-video ranges): A 3–13s; B 13–18s; C 18–31s; D 31–44s; E 44–64s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 16–17s; C1 X visible 20–21s; C2 X visible 25–26s; C3 X visible 29–30s; D0 X visible 34–35s; D1 X visible 38–39s; D2 X visible 42–43s; E0 X visible 46–47s; E1 X visible 51–52s; E2 X visible 55–56s; E3 X visible 60–61s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–13s; B 13–16s; C 16–28s; D 28–39s; E 39–56s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 8–9s; B0 X visible 15–16s; C1 X visible 19–20s; C2 X visible 22–23s; C3 X visible 26–27s; D0 X visible 30–31s; D1 X visible 34–35s; D2 X visible 37–38s; E0 X visible 41–42s; E1 X visible 45–46s; E2 X visible 48–49s; E3 X visible 52–53s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 8,497 pixels; >16 = 3,772 pixels.

E composer endpoint

Amplified differences: >0 = 8,852 pixels; >16 = 4,082 pixels.

plain · 390×844 · light

Before chapters (decoded-video ranges): A 2–12s; B 12–16s; C 16–30s; D 30–42s; E 42–61s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 15–16s; C1 X visible 19–20s; C2 X visible 23–24s; C3 X visible 27–28s; D0 X visible 32–33s; D1 X visible 36–37s; D2 X visible 40–41s; E0 X visible 45–46s; E1 X visible 49–50s; E2 X visible 53–54s; E3 X visible 57–58s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 2–13s; B 13–17s; C 17–30s; D 30–41s; E 41–60s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 16–17s; C1 X visible 20–21s; C2 X visible 23–24s; C3 X visible 27–28s; D0 X visible 32–33s; D1 X visible 36–37s; D2 X visible 39–40s; E0 X visible 43–44s; E1 X visible 48–49s; E2 X visible 52–53s; E3 X visible 56–57s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 25,641 pixels; >16 = 11,187 pixels.

E composer endpoint

Amplified differences: >0 = 26,761 pixels; >16 = 12,275 pixels.

plain · 390×844 · dark

Before chapters (decoded-video ranges): A 2–14s; B 14–18s; C 18–34s; D 34–47s; E 47–66s.

Before typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 16–17s; C1 X visible 20–21s; C2 X visible 25–26s; C3 X visible 30–31s; D0 X visible 37–38s; D1 X visible 41–42s; D2 X visible 45–46s; E0 X visible 49–50s; E1 X visible 54–55s; E2 X visible 58–59s; E3 X visible 62–63s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

After chapters (decoded-video ranges): A 3–13s; B 13–17s; C 17–30s; D 30–41s; E 41–60s.

After typing checkpoints: A0 X visible 5–6s; A1 X visible 9–10s; B0 X visible 16–17s; C1 X visible 20–21s; C2 X visible 23–24s; C3 X visible 27–28s; D0 X visible 32–33s; D1 X visible 36–37s; D2 X visible 40–41s; E0 X visible 44–45s; E1 X visible 48–49s; E2 X visible 52–53s; E3 X visible 56–57s. Seeds, Tab results, each C Shift+Enter, X, and deletion were also checked in decoded frames. Ranges identify a visible frame, not RPC completion.

Before keyboard sequence A–E — corrected

After keyboard sequence A–E — corrected

A rendered-message endpoint

Amplified differences: >0 = 25,653 pixels; >16 = 11,224 pixels.

E composer endpoint

Amplified differences: >0 = 26,767 pixels; >16 = 12,315 pixels.

Replacement recording verification

All replacement captures ran with the checkout fixed at ae038086a6. After web production bytes match 53ba38bb47. Each Before batch used the old helper only, then restored the exact saved After bytes (SHA-256 251b3e61cca09527c2cc9b74d2584aa536dbdfafdd16c76d429b6d09b344e605). No commits or persistent repository edits were made.

The prior independent audit validated all 32 original diff masks and pixel counts, and reproduced the E3 composer/message pixels exactly. Those stills and diff tables remain unchanged. The new endpoint screenshots were taken after the final hold and retained locally; git/context controls and caret timing can differ from the original stills.

Replacement canonical results match the original observations. All replacement persisted fixture runs are interrupted, have no startedAt, and have zero provider turns. Each sequence uses a new synthetic thread and the guarded defer_start → interrupt/holdQueue path. Failed early attempts were rejected, not uploaded.

Replacement observations · Decoded-frame verification

Final encoded composer frames across all 16 replacement clips

The verification used decoded whole-video frame sheets, inspecting all seeds and keyboard states; exact final source frames were decoded by frame index. Cropped frame sheets are inspection aids only: the uploaded recordings retain the complete viewport. Timestamp ranges are approximate visual indexes, not exact frame transition boundaries.

Limits and checks

Real web route verified. Hosted web/desktop share this editor but were not independently launched; 390px is responsive web, not native mobile. Unchanged selection/IME/literal-answer/autocomplete/code-block guards were not re-tested in this capture-only task. No provider, wire-contract, Settings-entry-point, command-palette, or remote-mode implementation changed. No repo-wide tests ran. Fixture syntax check and commit formatting hook passed. No merge-readiness verdict.

Native mobile uses a separate composer and is unaffected. The Electron shell and macOS/Windows hosts were not exercised; the edited keyboard logic is shared with web. No server, provider, persistence, or wire-contract changes.

Models: Claude Opus 5.5 and GPT-6.1 Sol; Claude and Codex harnesses through T3 Code.