synced blocks sibling selection

Objective: Fix Slate v2 Synced Blocks selection/navigation so synced content roots behave like ordinary sibling blocks for Shift+Arrow keyboard expansion and mouse drag/click selection across root boundaries. Complete only when focused browser repro rows for /examples/synced-blocks fail before the fix and pass after for cross-boundary Shift+ArrowLeft/Right/Up/Down, Cmd/Meta+Shift boundary movement where applicable, and mouse selection across before/synced/after blocks; affected shared behavior remains green for /examples/hidden-content-blocks and /examples/multi-root-document; focused Slate React/DOM package tests, owning package typecheck/lint, Chromium Playwright proof, local autoreview, and this plan's autogoal checker pass.

Flow mode: one-shot execution

Goal plan: docs/plans/2026-05-27-synced-blocks-sibling-selection.md

Template: docs/plans/templates/task.md

Primary template: docs/plans/templates/task.md

Applied packs:

browser (docs/plans/templates/packs/browser.md)
package-api (docs/plans/templates/packs/package-api.md)

Task source:

type: user bug report plus active autogoal
id / link: latest user prompt, /examples/synced-blocks
title: Synced Blocks must select like sibling blocks
acceptance criteria: Shift+Arrow and mouse selection through Synced Blocks feel like selecting ordinary adjacent paragraph blocks; hidden-content and multi-root shared behavior does not regress; public API stays stable unless evidence proves it cannot carry the behavior.

Completion threshold:

Focused Synced Blocks Playwright rows reproduce at least one pre-fix failure for Shift+Arrow and one pre-fix failure for mouse selection across content root boundaries.
The same rows pass after the fix, including forward and backward selection paths through before paragraph, first shared synced block, between paragraph, separate synced block, second shared copy, and after paragraph.
Existing hidden-content shifted-boundary behavior still passes.
Existing multi-root document root navigation/selection/history focused rows still pass.
Focused package tests for changed Slate React/DOM internals pass.
Owning package typecheck and scoped lint/format pass.
Local autoreview for .tmp/slate-v2 reports no accepted/actionable findings.
Release artifact decision is closed with patch changesets if published package behavior changed.
Task closure is legal only when the source-of-truth acceptance criteria are satisfied or explicitly narrowed, required verification evidence is recorded, code-review and release-artifact gates are closed when applicable, tracker/PR sync is complete or marked N/A with reason, and node .agents/rules/autogoal/scripts/check-complete.mjs docs/plans/2026-05-27-synced-blocks-sibling-selection.md passes.

Verification surface:

.tmp/slate-v2/playwright/integration/examples/synced-blocks.test.ts failing-then-passing rows for Shift+Arrow and mouse selection.
.tmp/slate-v2/playwright/integration/examples/hidden-content-blocks.test.ts shifted-boundary focused row.
.tmp/slate-v2/playwright/integration/examples/multi-root-document.test.ts affected focused rows.
Focused packages/slate-react/test/* contract tests for view-boundary, content-root navigation, keyboard input, selection, projected commands, or mouse/import behavior changed by this task.
.tmp/slate-v2: owning package typecheck, build if needed, scoped lint/format, and local autoreview.
plate-2: this plan and final autogoal checker.

Constraints:

Preserve existing user-facing behavior outside the task scope.
Prefer the durable ownership boundary over caller-by-caller patches.
Do not create PRs, comments, commits, or pushes unless the task/user/skill requires them.
Do not add broad ceremony when the task is trivial or docs-only.
Preserve public API: <Editable root>, slots.contentRoot, and slots.contentBoundary.
Keep one runtime editor with many views. Do not implement one editor per synced block.
Fix shared root-boundary selection ownership, not only the Synced Blocks example fixture.
Keep native-affordance claims honest. If a browser-native affordance cannot match sibling blocks, record the capability gap with proof.

Boundaries:

Source of truth: latest user prompt, active goal, prior unified view-boundary plan, and live .tmp/slate-v2 source/tests.
Allowed edit scope: .tmp/slate-v2/packages/slate-react/**, .tmp/slate-v2/packages/slate-dom/** if DOM selection/root helpers require it, .tmp/slate-v2/playwright/integration/examples/**, .tmp/slate-v2/site/examples/ts/synced-blocks.tsx only if fixture coverage genuinely needs more data, .tmp/slate-v2/.changeset/**, and this plan.
Browser surface: /examples/synced-blocks, plus regression proof on /examples/hidden-content-blocks and /examples/multi-root-document.
Tracker sync: N/A, no tracker item.
Non-goals: PR creation, Notion permission/server sync, slate-yjs adapter compatibility, product synced-block UI kits, and arbitrary public ViewSelection API exposure.

Blocked condition:

Block only if three distinct implementation/proof attempts show the current Slate model cannot make Synced Blocks match sibling block selection without a new public API or an unavoidable browser-native limitation, or if required .tmp/slate-v2 verification cannot run because of a persistent environment blocker that survives the repo-approved retry.

Task state:

task_type: browser-visible runtime bug / selection architecture fix
task_complexity: normal-to-major
current_phase: closeout
current_phase_status: complete
next_phase: final response
goal_status: ready for checker

Current verdict:

verdict: fixed in .tmp/slate-v2
confidence: high for covered desktop Chromium behavior; mobile/native affordance gaps remain explicitly classified by existing test matrix.
next owner: final response
reason: Synced Blocks now keeps one runtime editor with many mounted views, shares projected selection state across view editors, resolves repeated synced roots by visible owner, and passes keyboard, mouse, history, focus, package, typecheck, lint, browser, and autoreview gates.

Completion rule:

Do not call update_goal(status: complete) while any required checklist item remains unchecked. If an item does not apply, check it and add N/A: <reason>.
Do not call update_goal(status: complete) until every completion threshold above is satisfied, final handoff evidence is recorded, and node .agents/rules/autogoal/scripts/check-complete.mjs docs/plans/2026-05-27-synced-blocks-sibling-selection.md passes.
Do not create hook state for this goal. This file plus the active goal are the durable state.

Start Gates:

Gate	Applies	Evidence
Skill analysis before edits	yes	User invoked `autogoal`; loaded `autogoal`, `changeset`, and review rules during the lane.
Active goal checked or created	yes	`get_goal` confirmed active Synced Blocks sibling-selection goal for `docs/plans/2026-05-27-synced-blocks-sibling-selection.md`.
Source of truth read before edits	yes	Read latest prompt, active goal, prior unified view-boundary context, Synced Blocks example/tests, hidden-content tests, multi-root tests, and shared selection/navigation files.
Tracker comments and attachments read	no	N/A: no tracker item.
Video transcript evidence required	no	N/A: no video evidence.
`docs/solutions` checked for non-trivial existing-code work	yes	Searched solution notes for content-root, view-selection, Shift+Arrow, mouse selection, multi-root, and DOM selection ownership.
TDD decision before behavior change or bug fix	yes	Add failing Synced Blocks Playwright rows before runtime edits; browser proof is the primary behavior guard.
Branch decision for code-changing task	no	N/A: no branch/PR requested and repo says no proactive git hygiene.
Release artifact decision	yes	Published `slate-react` runtime behavior changed; added `.tmp/slate-v2/.changeset/synced-block-selection.md`.
Browser tool decision for browser surface	yes	Use owning `.tmp/slate-v2` Playwright Chromium rows for route proof.
PR expectation decision	no	N/A: no PR requested.
Tracker sync expectation decision	no	N/A: no tracker item.
Browser pack selected	yes	`browser` pack applied.
Browser route / app surface identified	yes	`/examples/synced-blocks`, with hidden-content and multi-root regression routes.
Browser tool decision recorded	yes	Playwright integration tests are the owning browser proof for `.tmp/slate-v2`.
Console/network caveat policy recorded	yes	Runtime/page errors fail targeted rows when relevant; final evidence records console/network caveat.
Package/API pack selected	yes	`package-api` pack applied.
Public surface or package boundary identified	yes	`slate-react` runtime behavior is in scope; `slate-dom` only if DOM selection bridge needs edits. Public API should stay stable.
Release artifact path selected	yes	`.tmp/slate-v2/.changeset/**` if package runtime behavior changes.
`changeset` skill loaded when `.changeset` is required	yes	Loaded `/Users/zbeyens/git/plate-2/.agents/skills/changeset/SKILL.md`; changeset uses one package, patch bump, user-impact wording.
Barrel/export impact decision recorded	yes	No package export or exported file-layout change; `pnpm brl` N/A.

Work Checklist:

Completion Gates:

Gate	Applies	Evidence
Named verification threshold	yes	Focused Synced Blocks rows passed; full affected Chromium sweep passed 37/37; package contracts, typecheck, lint, autoreview, changeset, and plan checker are recorded.
Bug reproduced before fix	yes	Pre-fix browser rows failed: repeated Shift+ArrowDown stayed at `[0,0]` instead of moving to `[1,0]`; mouse drag across root boundary produced native `"\n"`/no view selection; Cmd+Shift reverse wrote selection to the child copy instead of shared runtime.
Targeted behavior verification	yes	`PLAYWRIGHT_RETRIES=0 PLAYWRIGHT_WORKERS=1 bun playwright playwright/integration/examples/synced-blocks.test.ts --project=chromium --grep "keeps ordinary Shift\+Arrow
TypeScript or typed config changed	yes	`bun --filter slate-react typecheck && bun typecheck:site` passed in `.tmp/slate-v2`.
Package exports or file layout changed	no	N/A: no exports or exported file layout changed; `pnpm brl` not needed.
Package manifests, lockfile, or install graph changed	no	N/A: no manifests, lockfile, or install graph changed.
Agent rules or skills changed	no	N/A: no agent rules or skills changed.
Workspace authority proof	yes	All Slate runtime/browser checks ran from `.tmp/slate-v2`; autogoal checker runs from `plate-2`.
Browser surface changed	yes	Synced Blocks example changed; Chromium integration proof passed on target and sibling-risk routes.
Browser final proof	yes	Exact browser command below passed 37/37; no screenshot needed because repo-owned Playwright is the authoritative interaction proof.
CI-controlled template output changed	no	N/A: no template output touched.
Package behavior or public API changed	yes	Runtime behavior changed without public API change; `slate-react` patch changeset added.
Registry-only component work changed	no	N/A: no registry-only component work.
Docs or content changed	yes	This plan only; claims are command-backed and route-backed.
High-risk mini gate	yes	Failure mode was stale or wrong projected selection across root views; proof covers view selection, focus, history, keyboard, mouse, typecheck, browser, and autoreview.
Agent-native review for agent/tooling changes	no	N/A: no agent/tooling changes.
Local install corruption suspected	no	N/A: no local-env-rot failure shape appeared.
Autoreview for non-trivial implementation changes	yes	`PYTHONUNBUFFERED=1 /Users/zbeyens/git/plate-2/.agents/skills/autoreview/scripts/autoreview --mode local --no-web-search --thinking low --output /tmp/slate-v2-autoreview.txt --json-output /tmp/slate-v2-autoreview.json` passed clean after accepted findings were fixed.
PR create or update	no	N/A: no PR requested.
PR proof image hosting	no	N/A: no PR body.
Tracker sync-back	no	N/A: no tracker item.
Final handoff contract	yes	Filled below with outcome, proof, review, and caveats.
Final lint	yes	`bun biome check --fix` on 15 touched files passed with no fixes on final run.
Goal plan complete	yes	`node .agents/rules/autogoal/scripts/check-complete.mjs docs/plans/2026-05-27-synced-blocks-sibling-selection.md` to run after this update.
Browser interaction proof	yes	Full affected Chromium sweep passed 37/37.
Browser console/network check	yes	Existing runtime-error guards cover relevant Synced Blocks focus/path failures; final sweep reported no failing browser/runtime rows.
Browser final proof artifact	yes	Command output is the final proof artifact; no visual screenshot required for this behavior test.
Public API / package boundary proof	yes	Source audit: public `<Editable root>`, `slots.contentRoot`, and `slots.contentBoundary` stay intact; no exported barrels changed.
Release artifact classification	yes	Published runtime behavior delta in `slate-react`; not registry-only, docs-only, or agent-only.
Published package changeset	yes	`.tmp/slate-v2/.changeset/synced-block-selection.md` uses `"slate-react": patch`; no forbidden minor on core packages.
Registry changelog	no	N/A: no registry-only work.
No release artifact	no	N/A: release artifact exists.
Package typecheck/build/test	yes	64 Slate React contract tests passed; `slate-react` and site typechecks passed.
Barrel/export generation	no	N/A: no exports or exported file layout changed.

Phase / pass table:

Phase	Status	Evidence	Next
Intake and source read	complete	Read prompt, active goal, prior plans, examples, tests, and selection/navigation internals.	implementation complete
Implementation	complete	Shared view-selection store, owner-aware content-root navigation, mouse projected selection import, focus preservation, root-chrome cleanup, Synced Blocks fixture, tests, and changeset landed.	verification complete
Verification	complete	Unit/typecheck/lint/browser/autoreview gates passed.	closeout
PR / tracker sync	N/A	No PR or tracker requested.	final response
Closeout	complete	Plan updated; checker is the final remaining command.	final response

Findings:

Existing tests covered one-step projected Shift+Arrow but not repeated Shift+Arrow extension, Shift+ArrowLeft/Right, Cmd+Shift boundary movement, or mouse drag across root boundaries.
Synced Blocks repeated shared roots need owner identity from the current view, not the first owner of a shared child root.
Native mouse drag across separate contenteditable roots can resolve as newline or root-local DOM selection unless Slate imports DOM endpoints into a projected visible-order selection.
Ordinary Shift+Arrow inside a normal paragraph must remain native/model-local; root-local projected fallback is valid only while an existing projected view selection is being extended.
Direct focus after projected selection can export the collapsed model selection over the sidecar view selection unless focus avoids DOM model-sync while a projected selection exists.

Decisions and tradeoffs:

Keep the long-term architecture: one runtime editor, many root/view editors.
Store projected view selection by owning runtime editor so root clones and repeated synced copies share the same sidecar state.
Resolve content-root movement through the current mounted owner view before falling back to first owner for a child root.
Keep public API stable; Synced Blocks remains ordinary <Editable root> plus content-root slots.
Make nested content-root editors focusable by default (tabIndex = 0) because mouse and keyboard parity requires real focusable editing surfaces.
Clear projected sidecar selection whenever root chrome writes an ordinary root selection.
Preserve projected selections during internal focus by focusing the DOM element without running model-selection DOM export.

Implementation notes:

view-selection.ts keys read/write through setSlateViewSelectionStoreKey.
SlateRuntimeView and useSlateRootEditor register view editors under their runtime editor key.
content-root-navigation.ts supports repeated-root owner identity, horizontal and vertical projected extension, document-boundary Meta+Shift movement, and disables fresh root-local projected fallback unless extending an existing projected selection.
selection-controller.ts imports cross-root mouse DOM endpoints into projected selections before nested-focus early returns.
browser-handle.ts refocuses the attached editor element after model-owned insert/undo/redo commands so active synced copies keep focus.
focus-slate-editable.ts, keyboard-input-strategy.ts, and runtime-before-input-events.ts preserve projected selections during internal focus repair.
site/examples/ts/synced-blocks.tsx lets the block shell stay selectable and makes toolbar chrome user-select: none.

Review fixes:

Autoreview P1: ordinary Shift+Arrow inside paragraphs was intercepted by root-local projected movement. Fixed with allowRootLocalMovement gated on an existing projected selection; added normal paragraph Shift+Arrow browser row.
Autoreview P2: root chrome could restore a model selection while leaving a projected sidecar armed. Fixed by clearing view selection before root interaction writes normal selections; added useSlateRootChrome contract.
Autoreview P2: internal focus could export model selection over a projected selection on cloned root editors. Fixed focus helper to element-focus only while view selection exists; routed internal redirects through the helper; added focusSlateEditable contract.
Autoreview P2: shifted word-selection hotkeys ignored existing projected selections and fell through to stale collapsed model selection. Fixed projected word/line selection actions and added unit/browser coverage.

Error attempts:

Error / failed attempt	Count	Next different move	Resolution
Synced Blocks padding-coordinate Playwright row did not hit root interaction controller	1	Move stale-sidecar proof to `useSlateRootChrome` unit contract	Removed brittle row; unit contract now covers actual branch.
Default autoreview hung with no structured output	2	Keep Codex engine but lower reasoning effort and write output files	`--thinking low` produced one P2, then clean after fix.

Verification evidence:

.tmp/slate-v2/packages/slate-react: bun test:vitest test/content-root-navigation-contract.test.ts test/focus-slate-editable-contract.test.ts test/keyboard-input-strategy-contract.test.ts test/view-boundary-graph-contract.test.ts test/view-selection-contract.test.ts test/projected-command-contract.test.ts test/projected-clipboard-contract.test.ts test/use-slate-history.test.tsx test/root-interaction-resolver.test.ts test/browser-handle-contract.test.ts test/target-runtime-contract.tsx test/use-slate-root-chrome.test.tsx passed: 11 files, 64 tests.
.tmp/slate-v2: bun --filter slate-react typecheck && bun typecheck:site passed.
.tmp/slate-v2: bun biome check --fix packages/slate-react/src/editable/browser-handle.ts packages/slate-react/src/editable/content-root-navigation.ts packages/slate-react/src/editable/root-interaction-controller.ts packages/slate-react/src/editable/selection-controller.ts packages/slate-react/src/editable/keyboard-input-strategy.ts packages/slate-react/src/editable/runtime-before-input-events.ts packages/slate-react/src/hooks/focus-slate-editable.ts packages/slate-react/src/view-selection.ts packages/slate-react/src/components/slate.tsx packages/slate-react/src/hooks/use-slate-runtime.tsx packages/slate-react/src/components/editable-text-blocks.tsx packages/slate-react/test/focus-slate-editable-contract.test.ts packages/slate-react/test/use-slate-root-chrome.test.tsx site/examples/ts/synced-blocks.tsx playwright/integration/examples/synced-blocks.test.ts passed: 15 files checked, no fixes on final run.
.tmp/slate-v2: debug-marker scan over touched files returned no matches.
.tmp/slate-v2: focused Synced Blocks parity grep passed 5/5; additional word-extension row passed 1/1.
.tmp/slate-v2: PLAYWRIGHT_RETRIES=0 PLAYWRIGHT_WORKERS=1 bun playwright playwright/integration/examples/synced-blocks.test.ts playwright/integration/examples/hidden-content-blocks.test.ts playwright/integration/examples/multi-root-document.test.ts --project=chromium passed 37/37.
.tmp/slate-v2: PYTHONUNBUFFERED=1 /Users/zbeyens/git/plate-2/.agents/skills/autoreview/scripts/autoreview --mode local --no-web-search --thinking low --output /tmp/slate-v2-autoreview.txt --json-output /tmp/slate-v2-autoreview.json passed clean: no accepted/actionable findings.
.tmp/slate-v2: .changeset/synced-block-selection.md added for slate-react patch.

Final handoff contract:

PR line: N/A, no PR requested.
Issue / tracker line: N/A, no tracker item.
Confidence line: high for covered desktop Chromium keyboard/mouse/history/focus behavior.
Flow table:
- Reproduced: Shift+Arrow, mouse drag, and Cmd+Shift root-boundary failures were reproduced by new Synced Blocks rows before fixes.
- Verified: package contracts, typecheck, scoped lint, focused Synced Blocks rows, and 37-row affected browser sweep passed.
Browser check: 37/37 Chromium rows on Synced Blocks, Hidden Content Blocks, and Multi Root Document.
Outcome: Synced Blocks projected selection/navigation behaves like visible sibling blocks for covered keyboard and mouse flows while keeping shared state/history/focus.
Caveat: Native browser affordance limitations for projected selections remain classified by the existing affordance matrix; this task did not claim full native find/IME/mobile/screen-reader parity.
Design:
- Chosen boundary: shared runtime view-selection plus content-root navigation and selection controllers.
- Why not quick patch: example-only handlers would miss hidden-content, multi-root, history, repeated-copy, and command focus paths.
- Why not broader change: one runtime/many views already supports the product model; no public API rewrite was needed.
Verified: tests and review listed above.

Final handoff / sync:

PR: N/A, no PR requested.
Issue / tracker: N/A, no tracker item.
Browser proof: 37/37 Chromium rows on affected examples.
Caveats: projected-selection native affordances stay explicitly degraded where browsers cannot expose a true single native selection.

Timeline:

2026-05-26T23:16:21.598Z Task goal plan created.
2026-05-27T02:52:19+02:00 Replaced brittle root-padding Playwright row with useSlateRootChrome stale-sidecar contract.
2026-05-27T02:52:29+02:00 Focused Synced Blocks parity rows passed 5/5.
2026-05-27T02:53:00+02:00 Slate React contract suite passed 61 tests before focus-review fix.
2026-05-27T02:54:45+02:00 Affected browser sweep passed 36/36 before final focus-review fix.
2026-05-27T03:06:00+02:00 Autoreview accepted P2 for cloned-editor focus ignoring projected selection.
2026-05-27T03:08:01+02:00 Added and passed focusSlateEditable contract.
2026-05-27T03:09:05+02:00 Final Slate React contract suite passed 63 tests.
2026-05-27T03:09:40+02:00 slate-react and site typechecks passed.
2026-05-27T03:10:25+02:00 Final affected browser sweep passed 36/36.
2026-05-27T03:11:55+02:00 Final autoreview passed clean.
2026-05-27T03:19:50+02:00 Added projected word-selection unit coverage after autoreview finding.
2026-05-27T03:20:55+02:00 Final Slate React contract suite passed 64 tests.
2026-05-27T03:21:30+02:00 Final affected browser sweep passed 37/37.
2026-05-27T03:23:00+02:00 Final autoreview passed clean after word-selection fix.

Reboot status:

Question	Answer
Where am I?	Closeout, after implementation and verification.
Where am I going?	Run the autogoal checker, mark goal complete, final response.
What is the goal?	Make Synced Blocks select/navigate like sibling blocks while preserving hidden-content and multi-root behavior.
What have I learned?	See Findings and Decisions.
What have I done?	Implemented shared projected selection ownership, owner-aware navigation, mouse import, focus preservation, root-chrome cleanup, tests, changeset, and review fixes.

Open risks:

None known for covered desktop Chromium behavior. Residual browser-native affordance limitations remain intentionally documented by the projected affordance matrix.