refactor: extract editor dnd helpers

design/03-rust-web/process/3-20-browser-runtime-followup-checklist-v1.md

@@ -6,7 +6,7 @@
 
 ## 1. 目标
 
-在 `3-19` 已归档的基础上，继续把仍留在 Rust inline / 主壳大 runtime 中的浏览器行为切成可审计模块。Codex 维护本文件作为事实源，Reasonix 只承接短批次审计、窄范围实现或浏览器 smoke；每批最多 4 个 worker。
+在 `3-19` 已归档的基础上，继续把仍留在 Rust inline / 主壳大 runtime 中的浏览器行为切成可审计模块。Codex 维护本文件作为事实源，Reasonix 只承接短批次审计、窄范围实现或浏览器 smoke；每批最多 2 个 worker。
 
 ## 2. 本轮边界
 
@@ -63,7 +63,7 @@ UI / 浏览器可见项必须有真实浏览器截图或结构化 smoke 证据
 ## 6. 本轮执行记录
 
 - 2026-05-25：Codex 创建本续跑事实源。
-- 2026-05-25：修正执行约束：本文件遵循当前 goal 的“每批最多 4 个 worker”；实现 worker 必须在独立 worktree 产出候选 patch，Codex 复核后再选择性合入。
+- 2026-05-25：修正执行约束：本文件遵循当前 goal 的“每批最多 2 个 worker”；实现 worker 必须在独立 worktree 产出候选 patch，Codex 复核后再选择性合入。
 - 2026-05-25：下一批只派发 Worker B（local upload / filetree 下一刀只读审计）；Worker A/C/D 暂缓。
 - 2026-05-25：Reasonix local upload / filetree 只读审计尝试未产生 `result.json` / `process-handoff`，且运行期间出现额外 Batch A2 runner，主控已终止进程；该结果不作为正式 handoff 采纳。
   - 可参考的 transcript 结论：`fetchWithTimeout` 是低风险纯工具函数，可先迁入 `local-upload-runtime.js`；`uploadFileToMediaAsset` / `uploadFilesWithResolvedTarget` / `insertUploadedAssetIntoEditor` 仍与 API、editor 插入和 snapshot refresh 耦合，暂不迁。
@@ -92,7 +92,7 @@ UI / 浏览器可见项必须有真实浏览器截图或结构化 smoke 证据
   - 修改：`rust/crates/mnote-web/browser/document-conflict-panel-runtime.js`、`rust/crates/mnote-web/src/routes/web_shell.rs`。
   - 已验证：`node --check rust/crates/mnote-web/browser/document-conflict-panel-runtime.js`、`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/Cargo.toml -p mnote-web`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web document_conflict_panel_runtime_contains_dom_helpers -- --test-threads=1`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web mnote_browser_runtime_assets_are_explicitly_mounted -- --test-threads=1`。
   - 未完成：conflict merge / accept / keep 业务逻辑、document session lifecycle、secondary pane conflict smoke 仍未迁出；本轮未声称真实冲突 UI 全链路完成。
-- 2026-05-25：根据用户纠正，后续实现 worker 不能在主工作区直接修改；每批最多 4 个 worker，且必须采用独立 worktree 候选 patch 或明确只读任务。Codex 读取 Hindsight recall、`process-handoff.md/json`、`result.json`、diff 与验证证据后再选择性合入。
+- 2026-05-25：根据用户纠正，后续实现 worker 不能在主工作区直接修改；每批最多 2 个 worker，且必须采用独立 worktree 候选 patch 或明确只读任务。Codex 读取 Hindsight recall、`process-handoff.md/json`、`result.json`、diff 与验证证据后再选择性合入。
 - 2026-05-25：Codex 主控完成非本地 media upload API 小切片：`local-upload-runtime.js` 新增并导出 `uploadMediaAsset(file, plan, context)`，承接 `/api/media/upload` 的 FormData 构造、fetch 和响应解析；`layout.rs` 的 `uploadFileToMediaAsset` 仍负责 appendUploadedAssetRow、editor 插入和 `wolai:assets-changed` 事件分发，并保留完整 inline fallback。
   - 修改：`rust/crates/mnote-web/browser/local-upload-runtime.js`、`rust/crates/mnote-web/src/ssr/pages/layout.rs`。
   - 已验证：`node --check rust/crates/mnote-web/browser/local-upload-runtime.js`、`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/Cargo.toml -p mnote-web`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web local_upload_runtime_contains_editor_upload_context_helpers -- --test-threads=1`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web sidebar_upload_runtime_routes_local_markdown_assets_to_local_folder -- --test-threads=1`、`node scripts/task479-local-folder-markdown-resource-lifecycle-smoke.js`。
@@ -124,8 +124,12 @@ UI / 浏览器可见项必须有真实浏览器截图或结构化 smoke 证据
 - 2026-05-25：Batch E 派发异常并终止：Worker B 任务被重复启动为两个 runner / ACP 进程（`reasonix-2026-05-24T18-25-26-844Z-33ea4d58`、`reasonix-2026-05-24T18-26-04-453Z-5ff62e40`），同一 worktree `/mnt/Data1T/mnote-worktrees/0525-e-worker-b-3-20-conflict-diff-dom` 出现并发写入风险；Codex 已终止相关 Reasonix 进程，未读取到 `final.md`、`result.json`、`process-handoff.md/json`。原始未验证 diff 不直接采纳；后续采纳必须经过 Codex 独立复核、修正和验证。
 - 2026-05-25：Batch F 计划继续采用独立 worktree 候选 patch：Worker B 负责把 file tree 上传目标解析的纯 fallback / plan 归一化 helper 外置到 `filetree-runtime.js`；`layout.rs` 仍保留 async preflight 和完整 inline fallback，避免和当前 conflict panel 写集冲突。
 - 2026-05-25：Batch F Worker B 异常终止：run `reasonix-2026-05-24T18-39-34-442Z-d9e7ada1` 只产出 `prompt.md` / `memory-recall.json` / `reasonix-transcript.jsonl`，未产出 `final.md`、`result.json`、`process-handoff.md/json`，worktree 无 diff；transcript 停在 `ask_choice`，原因是 worker 误判任务书拼接了 Worker A / Worker B 两个任务并要求人工选择。Codex 已终止 runner / ACP，不采纳该 run。
-- 2026-05-25：Batch G 超限派发并终止：Worker B/C/D 三个 Reasonix runner 同时启动，超过当前 goal 的“每批最多 2 个 worker”；run `reasonix-2026-05-24T18-51-00-477Z-1307a1b4`、`reasonix-2026-05-24T18-51-00-504Z-2304f570`、`reasonix-2026-05-24T18-51-00-541Z-17d61f43` 均只有 `prompt.md` / `memory-recall.json` / `reasonix-transcript.jsonl`，无 handoff，worktree 无 diff；Codex 已终止 runner / ACP，不采纳该批。
+- 2026-05-25：Batch G 按用户纠正把 Worker B/C/D 分别派到独立 worktree，但三个 worker 同时启动，超过当前 goal 的“每批最多 2 个 worker”；三个 Reasonix run `reasonix-2026-05-24T18-51-00-477Z-1307a1b4`、`reasonix-2026-05-24T18-51-00-504Z-2304f570`、`reasonix-2026-05-24T18-51-00-541Z-17d61f43` 均只有 `prompt.md` / `memory-recall.json` / `reasonix-transcript.jsonl`，无 handoff/result/final，worktree 初始 diff 为空；Codex 不采纳这些 Reasonix run，只把独立 worktree 保留为 Codex 候选 patch 沙盒。
 - 2026-05-25：Codex 主控完成 filetree upload target fallback 小切片：`filetree-runtime.js` 新增并导出 `fileTreeUploadTargetFallback(detail, deps)`，承接同步 fallback / plan 归一化；`layout.rs` 的 `fallbackFileTreeUploadTarget` 优先委托 runtime，仍保留完整 inline fallback；async preflight、后端归属判定、`uploadFileToMediaAsset`、`uploadFilesWithResolvedTarget` 不迁。
   - 修改：`rust/crates/mnote-web/browser/filetree-runtime.js`、`rust/crates/mnote-web/src/ssr/pages/layout.rs`。
   - 已验证：`node --check rust/crates/mnote-web/browser/filetree-runtime.js`、`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/Cargo.toml -p mnote-web`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web filetree -- --test-threads=1`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web local_upload_runtime_contains_editor_upload_context_helpers -- --test-threads=1`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task479-local-folder-markdown-resource-lifecycle-smoke.js`。
   - 未完成：async preflight、`refreshLocalFolderSidebarSnapshot` / `appendUploadedAssetRow`、conflict action helpers、secondary pane conflict smoke 仍未迁出或覆盖。
+- 2026-05-25：Batch G Worker C 使用独立 worktree `/mnt/Data1T/mnote-worktrees/0525-g-worker-c-3-20-conflict-actions`；Reasonix run `reasonix-2026-05-24T18-51-00-504Z-2304f570` 无 handoff/result/final，且 transcript 停在 `ask_choice`，不采纳。Codex 随后在该 worktree 产出候选 patch，经复核后选择性移植到主工作区。
+  - 修改：`document-conflict-panel-runtime.js` 新增并导出 `runSessionConflictAction(action, deps)`，只负责 promise/catch 动作包装；`web_shell.rs` 仍持有 `acceptDiskVersion`、`keepCurrentEditorVersion`、`writeMergedConflictResult`、status 和重新渲染业务逻辑。
+  - 已验证：`node --check rust/crates/mnote-web/browser/document-conflict-panel-runtime.js`、`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/Cargo.toml -p mnote-web`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web document_conflict_panel_runtime_contains_dom_helpers -- --test-threads=1`、`cargo test --manifest-path rust/Cargo.toml -p mnote-web mnote_browser_runtime_assets_are_explicitly_mounted -- --test-threads=1`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task451-local-markdown-conflict-resolution-ui-smoke.js`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task479-local-folder-markdown-resource-lifecycle-smoke.js`。
+  - 未完成：`acceptDiskVersion` / `keepCurrentEditorVersion` / `writeMergedConflictResult` 业务逻辑、document session lifecycle、secondary pane conflict smoke 仍未迁出或覆盖。

design/05-editor-mainline/process/5-29-editor-runtime-followup-checklist-v1.md

@@ -67,7 +67,7 @@ UI / 浏览器可见项必须有真实浏览器截图或结构化 smoke 证据
   - 已迁函数：`node_is_within_root`、`active_editor_text_selection`、`has_active_text_selection`、`selection_summary`、`selection_has_rich_marks`。
   - 未迁：`SelectionPayload`、`selection_payload`、`send_selection_state*`、`selection_event_payload`，原因是仍依赖 bridge event、`HoveredBlockState` 和 runtime block id 边界。
   - 已验证：`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/spikes/leptos-tiptap-spike/Cargo.toml`、wasm release build、`wasm-bindgen`、`task488`、`task489`、CodeGraph pending 0。
-- 2026-05-25：执行口径修正：继续遵循当前 goal 的“每批最多 4 个 worker”；Reasonix 后续必须使用独立 worktree 或明确只读任务，完成后由 Codex 读取 handoff 并复核。
+- 2026-05-25：执行口径修正：继续遵循当前 goal 的“每批最多 2 个 worker”；Reasonix 后续必须使用独立 worktree 或明确只读任务，完成后由 Codex 读取 handoff 并复核。
 - 2026-05-25：Batch D 额外 runner 曾自动启动 Worker A / Worker B，未经过本轮主控计划确认；主控已终止相关 runner / ACP 进程，不采纳这些未受控 run。遗留 task 草稿暂不删除，后续如继续使用必须重新生成受控任务书。
 - 2026-05-25：Reasonix runner 异常：后续实现 run 未写 `result.json`、`process-handoff.md/json`，部分 transcript 停在工具调用阶段；Codex 不采纳其文字结论，只复核实际 diff。
 - 2026-05-25：Reasonix overlay / block menu 只读审计尝试未产生 `result.json` / `process-handoff`，且运行期间出现额外 Batch A2 runner，主控已终止进程；该结果不作为正式 handoff 采纳。
@@ -120,3 +120,12 @@ UI / 浏览器可见项必须有真实浏览器截图或结构化 smoke 证据
   - 修改：`rust/spikes/leptos-tiptap-spike/src/editor_runtime/block_menu_overlay.rs`、`rust/spikes/leptos-tiptap-spike/src/editor_runtime/mod.rs`、`rust/spikes/leptos-tiptap-spike/src/lib.rs`、generated island wasm/js/d.ts。
   - 已验证：`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/spikes/leptos-tiptap-spike/Cargo.toml`、wasm release build、`wasm-bindgen`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task489-block-menu-delete-undo-smoke.js`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task488-local-attachment-link-delete-undo-smoke.js`。
   - 未完成：`pointer_in_handle_corridor`、`drop_indicator_from_target` / `drop_indicator_from_point`、`sync_editor_overlay_state` / `try_sync_editor_overlay_state` 仍在 `lib.rs`。
+- 2026-05-25：Batch G Worker D 先按用户纠正使用独立 worktree `/mnt/Data1T/mnote-worktrees/0525-g-worker-d-5-29-block-dnd-helpers`；Reasonix run `reasonix-2026-05-24T18-51-00-541Z-17d61f43` 仅产出 `prompt.md` / `memory-recall.json` / `reasonix-transcript.jsonl`，无 handoff/result/final，worktree 初始 diff 为空，拒绝作为 Reasonix handoff 采纳。Codex 随后在该独立 worktree 产出候选 patch，经复核后选择性移植到主工作区。
+  - 修改：新增 `rust/spikes/leptos-tiptap-spike/src/editor_runtime/block_dnd.rs`，迁出 `pointer_in_handle_corridor` / `drop_indicator_from_target` 使用的纯几何 helper；`lib.rs` 仍保留 DOM 查询、signal 编排、拖拽事件和 HTML reorder 行为。
+  - 已验证：`cargo fmt --manifest-path rust/Cargo.toml --all --check`、`cargo check --manifest-path rust/spikes/leptos-tiptap-spike/Cargo.toml`、wasm release build、`wasm-bindgen`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task489-block-menu-delete-undo-smoke.js`、`NODE_PATH=/mnt/Data1T/mnote/node_modules node scripts/task488-local-attachment-link-delete-undo-smoke.js`。
+  - 未覆盖：`cargo test --manifest-path rust/spikes/leptos-tiptap-spike/Cargo.toml block_dnd -- --test-threads=1` 仍被既有 `STYLE` 测试编译错误阻断，未进入本次新增 helper 测试。
+  - 未完成：`drop_indicator_from_point` 的 DOM target lookup、拖拽 listener 编排、`sync_editor_overlay_state` / `try_sync_editor_overlay_state` 仍在 `lib.rs`。
+- 2026-05-25：Batch H 只派发 1 个只读 Reasonix worker 复核 block DnD helper 边界，使用独立 worktree `/mnt/Data1T/mnote-worktrees/0525-h-5-29-block-dnd-readonly`，run id `reasonix-2026-05-24T18-59-12-393Z-b5d95a7b`，并显式使用 `--no-memory-recall` 降低任务串线风险。
+  - Codex 已读取 Hindsight recall、`process-handoff.md/json`、`result.json`，并核对 worktree `git status --short` / `git diff --stat` 为空。
+  - 审计结论：只迁纯几何 helper 是合理边界；DOM 查询、`document.element_from_point`、event listener、Leptos signal 和拖拽重排行为继续留在 `lib.rs`。
+  - 主控裁决：采纳审计方向，但保留当前 `editor_runtime/block_dnd.rs` 的 `HandleCorridorGeometry` 参数结构，避免 Reasonix 建议的长参数列表降低可读性。

rust/crates/mnote-web/browser/document-conflict-panel-runtime.js

@@ -167,8 +167,24 @@ function populateSessionConflictDiffPanel(panel, context, deps) {
   });
 }
 
+function runSessionConflictAction(action, deps) {
+  deps = deps || {};
+  if (typeof action !== 'function') return;
+  try {
+    var result = action();
+    if (result && typeof result.then === 'function') {
+      result.catch(function(error) {
+        if (typeof deps.onError === 'function') deps.onError(error);
+      });
+    }
+  } catch (error) {
+    if (typeof deps.onError === 'function') deps.onError(error);
+  }
+}
+
 window.__mnoteDocumentConflictPanelRuntime = {
   clearSessionConflictSurface: clearSessionConflictSurface,
   createSessionConflictPanel: createSessionConflictPanel,
-  populateSessionConflictDiffPanel: populateSessionConflictDiffPanel
+  populateSessionConflictDiffPanel: populateSessionConflictDiffPanel,
+  runSessionConflictAction: runSessionConflictAction
 };

rust/crates/mnote-web/src/routes/web_shell.rs

@@ -2122,28 +2122,40 @@ pub(crate) fn render_editor_island_adapter_script() -> &'static str {
     await persistSession(session);
   };
 
+  const runSessionConflictAction = (action, onError) => {
+    const runtime = window.__mnoteDocumentConflictPanelRuntime;
+    if (runtime && typeof runtime.runSessionConflictAction === 'function') {
+      runtime.runSessionConflictAction(action, { onError });
+      return;
+    }
+    try {
+      const result = action();
+      if (result && typeof result.then === 'function') result.catch(onError);
+    } catch (error) {
+      onError(error);
+    }
+  };
+
   const renderSessionConflictSurface = (session, message) => {
     clearSessionConflictSurface(session);
     sessionViews(session).forEach((view) => {
       const host = view.runtimeDescriptor.root.closest('.document-pane') || view.runtimeDescriptor.root;
       if (!(host instanceof HTMLElement)) return;
       const runtime = window.__mnoteDocumentConflictPanelRuntime;
+      const handleConflictActionError = (error) => {
+        setSessionStatus(session, 'external-change-conflict', error instanceof Error ? error.message : String(error));
+        renderSessionConflictSurface(session, error instanceof Error ? error.message : String(error));
+      };
       let panel = null;
       if (runtime && typeof runtime.createSessionConflictPanel === 'function') {
         panel = runtime.createSessionConflictPanel(session, message, {
           externalConflictMessage,
           conflictSourceLabel,
           onAcceptDisk: () => {
-            acceptDiskVersion(session).catch((error) => {
+            runSessionConflictAction(() => acceptDiskVersion(session), handleConflictActionError);
-              setSessionStatus(session, 'external-change-conflict', error instanceof Error ? error.message : String(error));
-              renderSessionConflictSurface(session, error instanceof Error ? error.message : String(error));
-            });
           },
           onKeepCurrent: () => {
-            keepCurrentEditorVersion(session).catch((error) => {
+            runSessionConflictAction(() => keepCurrentEditorVersion(session), handleConflictActionError);
-              setSessionStatus(session, 'external-change-conflict', error instanceof Error ? error.message : String(error));
-              renderSessionConflictSurface(session, error instanceof Error ? error.message : String(error));
-            });
           },
           onOpenDiff: (_session, createdPanel) => {
             openConflictDiffPanel(session, createdPanel);
@@ -2189,16 +2201,10 @@ pub(crate) fn render_editor_island_adapter_script() -> &'static str {
         panel.append(heading, text, meta, actions, diffPanel);
 
         acceptDisk.addEventListener('click', () => {
-          acceptDiskVersion(session).catch((error) => {
+          runSessionConflictAction(() => acceptDiskVersion(session), handleConflictActionError);
-            setSessionStatus(session, 'external-change-conflict', error instanceof Error ? error.message : String(error));
-            renderSessionConflictSurface(session, error instanceof Error ? error.message : String(error));
-          });
         });
         keepCurrent.addEventListener('click', () => {
-          keepCurrentEditorVersion(session).catch((error) => {
+          runSessionConflictAction(() => keepCurrentEditorVersion(session), handleConflictActionError);
-            setSessionStatus(session, 'external-change-conflict', error instanceof Error ? error.message : String(error));
-            renderSessionConflictSurface(session, error instanceof Error ? error.message : String(error));
-          });
         });
         openDiff.addEventListener('click', () => {
           openConflictDiffPanel(session, panel);
@@ -5659,6 +5665,9 @@ mod tests {
         assert!(DOCUMENT_CONFLICT_PANEL_RUNTIME_JS.contains("onUseCurrent"));
         assert!(DOCUMENT_CONFLICT_PANEL_RUNTIME_JS.contains("onUseDisk"));
         assert!(DOCUMENT_CONFLICT_PANEL_RUNTIME_JS.contains("onSaveMerge"));
+        assert!(DOCUMENT_CONFLICT_PANEL_RUNTIME_JS.contains("function runSessionConflictAction"));
+        assert!(DOCUMENT_CONFLICT_PANEL_RUNTIME_JS
+            .contains("runSessionConflictAction: runSessionConflictAction"));
     }
 
     #[tokio::test]

rust/spikes/leptos-tiptap-spike/src/editor_runtime/block_dnd.rs

@@ -0,0 +1,92 @@
+//! Block handle 拖拽命中的纯几何 helper。
+//!
+//! 本模块不查询 DOM、不处理 Leptos signal，也不分发 editor command；
+//! 调用方负责传入已经从页面中读取的坐标。
+
+use crate::editor_runtime::block_hover_state::DropPlacement;
+
+pub(crate) struct HandleCorridorGeometry {
+    pub(crate) stage_left: f64,
+    pub(crate) stage_top: f64,
+    pub(crate) block_left: f64,
+    pub(crate) block_top: f64,
+    pub(crate) block_bottom: f64,
+    pub(crate) handle_left: f64,
+    pub(crate) handle_right: f64,
+}
+
+pub(crate) fn pointer_in_handle_corridor_geometry(
+    client_x: i32,
+    client_y: i32,
+    geometry: &HandleCorridorGeometry,
+) -> bool {
+    let x = f64::from(client_x) - geometry.stage_left;
+    let y = f64::from(client_y) - geometry.stage_top;
+    let corridor_left = (geometry.handle_left - 12.0).min(geometry.block_left);
+    let corridor_right = (geometry.block_left + 18.0).max(geometry.handle_right + 12.0);
+
+    x >= corridor_left
+        && x <= corridor_right
+        && y >= geometry.block_top - 18.0
+        && y <= geometry.block_bottom + 18.0
+}
+
+pub(crate) fn drop_placement_from_block_point(
+    client_y: i32,
+    block_top: f64,
+    block_height: f64,
+) -> DropPlacement {
+    let midpoint = block_top + (block_height / 2.0);
+    if f64::from(client_y) <= midpoint {
+        DropPlacement::Before
+    } else {
+        DropPlacement::After
+    }
+}
+
+pub(crate) fn drop_indicator_top(
+    stage_top: f64,
+    block_top: f64,
+    block_bottom: f64,
+    placement: DropPlacement,
+) -> f64 {
+    match placement {
+        DropPlacement::Before => block_top - stage_top,
+        DropPlacement::After => block_bottom - stage_top,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn pointer_corridor_accepts_handle_lane_and_block_edge() {
+        let geometry = HandleCorridorGeometry {
+            stage_left: 100.0,
+            stage_top: 20.0,
+            block_left: 140.0,
+            block_top: 40.0,
+            block_bottom: 80.0,
+            handle_left: 108.0,
+            handle_right: 130.0,
+        };
+
+        assert!(pointer_in_handle_corridor_geometry(118, 80, &geometry));
+        assert!(pointer_in_handle_corridor_geometry(250, 80, &geometry));
+        assert!(!pointer_in_handle_corridor_geometry(90, 80, &geometry));
+        assert!(!pointer_in_handle_corridor_geometry(118, 28, &geometry));
+    }
+
+    #[test]
+    fn drop_placement_splits_block_at_midpoint() {
+        assert_eq!(
+            drop_placement_from_block_point(50, 40.0, 20.0),
+            DropPlacement::Before
+        );
+        assert_eq!(
+            drop_placement_from_block_point(51, 40.0, 20.0),
+            DropPlacement::After
+        );
+    }
+}

rust/spikes/leptos-tiptap-spike/src/editor_runtime/mod.rs

@@ -1,5 +1,6 @@
 pub(crate) mod attachment_links;
 pub(crate) mod attachment_upload;
+pub(crate) mod block_dnd;
 pub(crate) mod block_hover_state;
 pub(crate) mod block_menu_document;
 pub(crate) mod block_menu_overlay;

rust/spikes/leptos-tiptap-spike/src/lib.rs

@@ -21,12 +21,16 @@ use web_sys::{
 };
 
 use editor_runtime::attachment_upload::dispatch_editor_upload_request;
+use editor_runtime::block_dnd::{
+    drop_indicator_top, drop_placement_from_block_point, pointer_in_handle_corridor_geometry,
+    HandleCorridorGeometry,
+};
 use editor_runtime::block_menu_overlay;
 use editor_runtime::block_menu_legacy_html::{
     duplicate_top_level_block_html, reorder_top_level_block_html,
 };
 use editor_runtime::block_hover_state::{
-    BlockMenuLayout, DropIndicatorState, DropPlacement, HoveredBlockState, PendingDragState,
+    BlockMenuLayout, DropIndicatorState, HoveredBlockState, PendingDragState,
 };
 use editor_runtime::command_sync::{
     read_editor_snapshot, sync_editor_outputs, sync_persisted_editor_command,
@@ -5416,8 +5420,6 @@ fn pointer_in_handle_corridor(client_x: i32, client_y: i32, block: &HoveredBlock
     let block_left = block_rect.left() - stage_rect.left();
     let block_top = block_rect.top() - stage_rect.top();
     let block_bottom = block_rect.bottom() - stage_rect.top();
-    let x = f64::from(client_x) - stage_rect.left();
-    let y = f64::from(client_y) - stage_rect.top();
     let handle_left = handle_rect
         .as_ref()
         .map(|rect| rect.left() - stage_rect.left())
@@ -5426,10 +5428,20 @@ fn pointer_in_handle_corridor(client_x: i32, client_y: i32, block: &HoveredBlock
         .as_ref()
         .map(|rect| rect.right() - stage_rect.left())
         .unwrap_or_else(|| handle_left + HANDLE_TRIGGER_WIDTH);
-    let corridor_left = (handle_left - 12.0).min(block_left);
-    let corridor_right = (block_left + 18.0).max(handle_right + 12.0);
 
-    x >= corridor_left && x <= corridor_right && y >= block_top - 18.0 && y <= block_bottom + 18.0
+    pointer_in_handle_corridor_geometry(
+        client_x,
+        client_y,
+        &HandleCorridorGeometry {
+            stage_left: stage_rect.left(),
+            stage_top: stage_rect.top(),
+            block_left,
+            block_top,
+            block_bottom,
+            handle_left,
+            handle_right,
+        },
+    )
 }
 
 fn drop_indicator_from_target(
@@ -5442,16 +5454,8 @@ fn drop_indicator_from_target(
     let stage = editor_stage_element()?;
     let block_rect = block.get_bounding_client_rect();
     let stage_rect = stage.get_bounding_client_rect();
-    let midpoint = block_rect.top() + (block_rect.height() / 2.0);
+    let placement = drop_placement_from_block_point(client_y, block_rect.top(), block_rect.height());
-    let placement = if f64::from(client_y) <= midpoint {
+    let top = drop_indicator_top(stage_rect.top(), block_rect.top(), block_rect.bottom(), placement);
-        DropPlacement::Before
-    } else {
-        DropPlacement::After
-    };
-    let top = match placement {
-        DropPlacement::Before => block_rect.top() - stage_rect.top(),
-        DropPlacement::After => block_rect.bottom() - stage_rect.top(),
-    };
 
     Some(DropIndicatorState {
         index: hovered.index,