fix(mobile): a caret move in one composer no longer moves another draft's insert point

apps/mobile/src/features/threads/use-composer-command-menu.test.ts

@@ -9,8 +9,8 @@ vi.mock("../../state/queries", () => ({
 }));
 vi.mock("../../state/use-composer-drafts", () => ({
   getComposerDraftSnapshot: vi.fn(),
-  readComposerDraftSelection: vi.fn(),
   setComposerDraftContext: vi.fn(),
+  useComposerDraftSelection: vi.fn(),
 }));
 vi.mock("../../lib/uuid", () => ({ uuidv4: () => "context-id" }));
 vi.mock("../../state/server", () => ({
@@ -23,8 +23,44 @@ vi.mock("../../state/server", () => ({
 import {
   buildComposerSlashCommandItems,
   resolveComposerCommandSelection,
+  resolveComposerMenuSelection,
 } from "./use-composer-command-menu";
 
+describe("resolveComposerMenuSelection", () => {
+  it("prefers the caret an insertion placed in the current draft text", () => {
+    expect(
+      resolveComposerMenuSelection({
+        draftMessage: "hello @chip ",
+        ownerKey: "draft-a",
+        inserted: { start: 12, end: 12 },
+        local: { ownerKey: "draft-a", start: 2, end: 2 },
+      }),
+    ).toEqual({ start: 12, end: 12 });
+  });
+
+  it("clamps the composer's own caret when the draft shrinks", () => {
+    expect(
+      resolveComposerMenuSelection({
+        draftMessage: "hi",
+        ownerKey: "draft-a",
+        inserted: null,
+        local: { ownerKey: "draft-a", start: 5, end: 9 },
+      }),
+    ).toEqual({ start: 2, end: 2 });
+  });
+
+  it("starts at the end of the draft after switching owners", () => {
+    expect(
+      resolveComposerMenuSelection({
+        draftMessage: "other draft",
+        ownerKey: "draft-b",
+        inserted: null,
+        local: { ownerKey: "draft-a", start: 1, end: 1 },
+      }),
+    ).toEqual({ start: 11, end: 11 });
+  });
+});
+
 describe("mobile slash commands", () => {
   const antigravity = {
     driver: ProviderDriverKind.make("antigravity"),

apps/mobile/src/features/threads/use-composer-command-menu.ts

@@ -17,8 +17,8 @@ import { pullRequestComposerContext, threadComposerContext } from "../../lib/com
 import { uuidv4 } from "../../lib/uuid";
 import {
   getComposerDraftSnapshot,
-  readComposerDraftSelection,
   setComposerDraftContext,
+  useComposerDraftSelection,
 } from "../../state/use-composer-drafts";
 import { USAGE_LIMITS_COMMAND } from "@t3tools/shared/usageLimits";
 import {
@@ -43,7 +43,7 @@ import {
 } from "@t3tools/client-runtime/providerSkills";
 import { useAtomRefresh } from "@effect/atom-react";
 import { Atom } from "effect/reactivity";
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useState } from "react";
 
 import type { ComposerEditorSelection } from "../../components/ComposerEditor";
 import { serverEnvironment } from "../../state/server";
@@ -68,6 +68,27 @@ function composerSelectionAtEnd(draftMessage: string): ComposerEditorSelection {
   return { start: draftMessage.length, end: draftMessage.length };
 }
 
+/**
+ * A caret placed by an insertion (chips, pasted context) wins while the draft
+ * still has the text it was placed in. Otherwise the composer's own caret is
+ * clamped to the draft, and a caret from another owner starts at the end.
+ */
+export function resolveComposerMenuSelection(input: {
+  readonly draftMessage: string;
+  readonly ownerKey: string | null;
+  readonly inserted: ComposerEditorSelection | null;
+  readonly local: {
+    readonly ownerKey: string | null;
+    readonly start: number;
+    readonly end: number;
+  };
+}): ComposerEditorSelection {
+  if (input.inserted) return input.inserted;
+  if (input.local.ownerKey !== input.ownerKey) return composerSelectionAtEnd(input.draftMessage);
+  const length = input.draftMessage.length;
+  return { start: Math.min(input.local.start, length), end: Math.min(input.local.end, length) };
+}
+
 export function buildComposerSlashCommandItems(input: {
   readonly query: string;
   readonly atMessageStart: boolean;
@@ -212,34 +233,21 @@ export function useComposerCommandMenu({
   readonly onUpdateInteractionMode?: (mode: ProviderInteractionMode) => void;
   readonly onUsageLimits?: () => void;
 }) {
-  const [selection, setSelection] = useState(() => composerSelectionAtEnd(draftMessage));
+  const [localSelection, setLocalSelection] = useState(() => ({
+    ownerKey,
+    ...composerSelectionAtEnd(draftMessage),
+  }));
   // Thread mentions rank by recency as of when the composer mounted.
   const [now] = useState(() => Date.now());
-  const previousOwnerKeyRef = useRef(ownerKey);
-  useEffect(() => {
-    const inserted = ownerKey ? readComposerDraftSelection(ownerKey, draftMessage) : null;
-    if (inserted) {
-      // oxlint-disable-next-line react/set-state-in-effect -- Applies a selection inserted into the draft store by another surface.
-      setSelection((current) =>
-        current.start === inserted.start && current.end === inserted.end ? current : inserted,
-      );
-      return;
-    }
-    const end = draftMessage.length;
-    setSelection((current) => {
-      const start = Math.min(current.start, end);
-      const selectionEnd = Math.min(current.end, end);
-      if (start === current.start && selectionEnd === current.end) {
-        return current;
-      }
-      return { start, end: selectionEnd };
-    });
-  }, [draftMessage, ownerKey]);
-  useEffect(() => {
-    if (previousOwnerKeyRef.current === ownerKey) return;
-    previousOwnerKeyRef.current = ownerKey;
-    setSelection(composerSelectionAtEnd(draftMessage));
-  }, [draftMessage, ownerKey]);
+  const insertedSelection = useComposerDraftSelection(ownerKey, draftMessage);
+  const selection = resolveComposerMenuSelection({
+    draftMessage,
+    ownerKey,
+    inserted: insertedSelection,
+    local: localSelection,
+  });
+  const setSelection = (next: ComposerEditorSelection) =>
+    setLocalSelection({ ownerKey, start: next.start, end: next.end });
 
   const skills = selectedProviderStatus
     ? resolveProviderSkillsForCwd(selectedProviderStatus, projectCwd)

apps/mobile/src/state/use-composer-drafts.test.ts

@@ -981,6 +981,37 @@ describe("mobile composer drafts", () => {
     expect(getComposerDraftSnapshot(draftKey).context).toBeUndefined();
   });
 
+  it("keeps each draft's caret when another composer moves its own caret", () => {
+    const threadKey = "caret-environment:caret-thread";
+    const newTaskKey = "caret-environment:new-task:caret-draft";
+    setComposerDraftText(threadKey, "Fix this next");
+    setComposerDraftText(newTaskKey, "Another task");
+    rememberComposerDraftSelection(threadKey, "Fix this next", { start: 4, end: 8 });
+    rememberComposerDraftSelection(newTaskKey, "Another task", { start: 2, end: 2 });
+    insertComposerDraftContext(threadKey, {
+      text: "[Build output](t3-context://v1/terminal/caret-terminal)",
+      context: {
+        version: 1,
+        records: [
+          {
+            version: 1,
+            kind: "terminal",
+            contextId: ComposerContextId.make("caret-terminal"),
+            label: "Build output",
+            terminalId: "main",
+            terminalLabel: "Terminal",
+            lineStart: 1,
+            lineEnd: 1,
+            text: "Build failed",
+          },
+        ],
+      },
+    });
+    expect(getComposerDraftSnapshot(threadKey).text).toBe(
+      "Fix [Build output](t3-context://v1/terminal/caret-terminal) next",
+    );
+  });
+
   it("releases videos rejected by the live draft limit and keeps accepted files", async () => {
     const outboxLoad = vi.spyOn(threadOutboxManager, "load").mockResolvedValue(true);
     onTestFinished(() => outboxLoad.mockRestore());

apps/mobile/src/state/use-composer-drafts.ts

@@ -88,26 +88,57 @@ export function setComposerContextImporting(draftKey: string, importing: boolean
   appAtomRegistry.set(composerContextImportsAtom, next);
 }
 
-let lastComposerSelection: { draftKey: string; text: string; start: number; end: number } | null =
-  null;
+interface ComposerDraftSelection {
+  readonly text: string;
+  readonly start: number;
+  readonly end: number;
+}
+
+// Keyed by draft so a caret move in one composer neither replaces another draft's caret
+// nor notifies its readers. Kept alive so the caret survives the composer unmounting.
+const composerDraftSelectionAtom = Atom.family((_draftKey: string) =>
+  Atom.make<ComposerDraftSelection | null>(null).pipe(
+    Atom.keepAlive,
+    Atom.withLabel("mobile:composer-draft-selection"),
+  ),
+);
+const NO_COMPOSER_DRAFT_SELECTION_ATOM = Atom.make<ComposerDraftSelection | null>(null);
 
 export function rememberComposerDraftSelection(
   draftKey: string,
   text: string,
   selection: { start: number; end: number },
 ): void {
-  lastComposerSelection = { draftKey, text, ...selection };
+  appAtomRegistry.set(composerDraftSelectionAtom(draftKey), { text, ...selection });
+}
+
+function matchingComposerDraftSelection(
+  selection: ComposerDraftSelection | null,
+  text: string,
+): { start: number; end: number } | null {
+  if (selection?.text !== text) return null;
+  return { start: selection.start, end: selection.end };
 }
 
 /** Read the post-chip-insertion selection or the editor restores the pre-insert caret before the chip. */
-export function readComposerDraftSelection(
+function readComposerDraftSelection(
   draftKey: string,
   text: string,
 ): { start: number; end: number } | null {
-  if (lastComposerSelection?.draftKey !== draftKey || lastComposerSelection.text !== text) {
-    return null;
-  }
-  return { start: lastComposerSelection.start, end: lastComposerSelection.end };
+  return matchingComposerDraftSelection(
+    appAtomRegistry.get(composerDraftSelectionAtom(draftKey)),
+    text,
+  );
+}
+
+export function useComposerDraftSelection(
+  draftKey: string | null,
+  text: string,
+): { start: number; end: number } | null {
+  const selection = useAtomValue(
+    draftKey === null ? NO_COMPOSER_DRAFT_SELECTION_ATOM : composerDraftSelectionAtom(draftKey),
+  );
+  return draftKey === null ? null : matchingComposerDraftSelection(selection, text);
 }
 
 export interface ComposerDraftInsertion {
@@ -133,8 +164,7 @@ function contextInsertionRange(
   draft: ComposerDraft,
   target?: ComposerDraftInsertion,
 ) {
-  const captured =
-    target ?? (lastComposerSelection?.draftKey === draftKey ? lastComposerSelection : null);
+  const captured = target ?? appAtomRegistry.get(composerDraftSelectionAtom(draftKey));
   // Append after text edits during writes; caret-only moves preserve the captured insertion range.
   const selection = captured?.text === draft.text ? captured : null;
   const start = Math.max(0, Math.min(selection?.start ?? draft.text.length, draft.text.length));
@@ -307,12 +337,10 @@ function draftWithInsertedContext(
   for (const record of content.context.records) records.set(record.contextId, record);
   const context = referencedComposerContext(text, { version: 1, records: [...records.values()] });
   if ((context?.records.length ?? 0) > COMPOSER_CONTEXT_MAX_RECORDS) return null;
-  lastComposerSelection = {
-    draftKey,
-    text,
+  rememberComposerDraftSelection(draftKey, text, {
     start: start + insertion.length,
     end: start + insertion.length,
-  };
+  });
   return withReferencedContextFiles(draft, text, context);
 }