diff --git a/src/client/conversation-draft.ts b/src/client/conversation-draft.ts
index 9047054..f6c8fef 100644
--- a/src/client/conversation-draft.ts
+++ b/src/client/conversation-draft.ts
@@ -1,16 +1,88 @@
 /**
- * Append text to the current session's composer draft through the
+ * Insert text into the current session's composer draft through the
  * conversation service — the shared path behind the explorer's @-reference
  * button and the viewer selection popup. The service is resolved lazily
  * through `ctx.get` (the inject-free read the app's own plugins use); a
  * missing service or scope degrades to a logged no-op, never a crash.
+ *
+ * Insert position (fixes upstream issue #425): the draft store only exposes
+ * the whole string (`getSnapshot().draft` + `setDraft(text)`) — there is no
+ * caret API on the conversation service. The composer's `<textarea>` keeps
+ * its last selection even while unfocused, so the live caret is probed from
+ * the DOM (guarded by a value-sync check), and the text is spliced at that
+ * position, replacing any live selection — with whitespace-aware joins, an
+ * insert into the middle of a sentence keeps single-space separation like
+ * the append path. An unknown/stale caret falls back to appending at the
+ * end (the pre-fix behavior).
  */
 import type { Context, SidebarConversation } from '../context-types.ts'
 
+/** A resolved composer caret/selection in draft coordinates. */
+export interface DraftCaret {
+  start: number
+  end: number
+}
+
 /**
- * Append `text` to the session's composer draft (space-separated, like the
- * @-mentions). Returns false — and logs — when the conversation service or
- * the session scope is unavailable.
+ * Splice `text` into `draft` at `caret` (replacing any live selection) with
+ * whitespace-aware joins. `caret === null` (position unknown) appends at the
+ * end, exactly like the original behavior. Pure string math — unit-tested
+ * directly.
+ */
+export function insertAtCaret(draft: string, text: string, caret: DraftCaret | null): string {
+  if (caret === null || draft === '') {
+    return draft.trim() === '' ? text : `${draft} ${text}`
+  }
+  const prefix = draft.slice(0, caret.start)
+  const suffix = draft.slice(caret.end)
+  if (prefix === '' && suffix === '') return text
+  // One separating space, but never doubled against adjacent whitespace
+  // (or the string edges) — mirrors how typing in the middle of a sentence
+  // behaves.
+  const left = prefix === '' || /\s$/.test(prefix) ? '' : ' '
+  const right = suffix === '' || /^\s/.test(suffix) ? '' : ' '
+  return `${prefix}${left}${text}${right}${suffix}`
+}
+
+/**
+ * Resolve the composer's live caret from its DOM `<textarea>`. The draft
+ * store has no caret API, so the sidebar reads the composed input's selection
+ * directly; the value-sync check (`el.value === draft`) discards stale or
+ * wrong-composer reads — a caret must never be applied against a draft it
+ * was not measured on.
+ *
+ * Returns null when the composer is missing, disabled/read-only, out of
+ * sync with the store draft, or has no measurable selection (jsdom/odd
+ * hosts report null selectionStart/End).
+ */
+export function probeComposerCaret(draft: string): DraftCaret | null {
+  if (typeof document === 'undefined') return null
+  // The active composer lives in the conversation column; prefer its
+  // `data-phase`-tagged textarea (the composer's marker), falling back to
+  // any textarea in the column, then to a bare data-phase textarea (older
+  // host layouts without the column attribute).
+  const column = document.querySelector('#root [data-slot="conversation"]')
+  const find = (scope: ParentNode): HTMLTextAreaElement | null =>
+    scope.querySelector('textarea[data-phase]') ?? scope.querySelector('textarea')
+  const el = column !== null
+    ? find(column)
+    : document.querySelector<HTMLTextAreaElement>('textarea[data-phase]')
+  if (el === null || el.disabled || el.readOnly) return null
+  if (el.value !== draft) return null
+  let start = el.selectionStart
+  let end = el.selectionEnd
+  if (typeof start !== 'number' || typeof end !== 'number') return null
+  if (!Number.isFinite(start) || !Number.isFinite(end)) return null
+  start = Math.max(0, Math.min(start, draft.length))
+  end = Math.max(start, Math.min(end, draft.length))
+  return { start, end }
+}
+
+/**
+ * Insert `text` into the session's composer draft at the composer's live
+ * caret (see {@link probeComposerCaret}), falling back to appending at the
+ * end when the caret cannot be resolved. Returns false — and logs — when the
+ * conversation service or the session scope is unavailable.
  */
 export function appendToDraft(ctx: Context, sessionId: string, text: string): boolean {
   try {
@@ -20,10 +92,10 @@ export function appendToDraft(ctx: Context, sessionId: string, text: string): bo
     if (conversation === undefined) return false
     const input = conversation.input.for(actx)
     const draft = input.state.getSnapshot().draft
-    input.setDraft(draft.trim() === '' ? text : `${draft} ${text}`)
+    input.setDraft(insertAtCaret(draft, text, probeComposerCaret(draft)))
     return true
   } catch (error) {
     console.warn('[dsh-better-sidebar] draft insert failed:', error)
     return false
   }
-}
+}
\ No newline at end of file
diff --git a/tests/conversation-draft.spec.ts b/tests/conversation-draft.spec.ts
new file mode 100644
index 0000000..5121767
--- /dev/null
+++ b/tests/conversation-draft.spec.ts
@@ -0,0 +1,122 @@
+/**
+ * conversation-draft spec — the caret-resolved composer insertion (upstream
+ * issue #425 ②). `insertAtCaret` is pure string math (splice with
+ * whitespace-aware joins); `probeComposerCaret` reads the live composer
+ * `<textarea>` selection out of the DOM, guarded by a value-sync check so a
+ * stale or wrong-composer caret is never applied.
+ */
+// @vitest-environment jsdom
+import { afterEach, describe, expect, it } from 'vitest'
+import { insertAtCaret, probeComposerCaret } from '../src/client/conversation-draft.ts'
+
+/**
+ * Mount a fake composer textarea inside the DSH conversation column
+ * (`#root [data-slot="conversation"] textarea[data-phase]`).
+ */
+function mountComposer(draft: string, selectionStart: number, selectionEnd: number): HTMLTextAreaElement {
+  const root = document.createElement('div')
+  root.id = 'root'
+  const column = document.createElement('div')
+  column.setAttribute('data-slot', 'conversation')
+  const textarea = document.createElement('textarea')
+  textarea.setAttribute('data-phase', 'plain')
+  textarea.value = draft
+  textarea.setSelectionRange(selectionStart, selectionEnd)
+  column.append(textarea)
+  root.append(column)
+  document.body.append(root)
+  return textarea
+}
+
+afterEach(() => {
+  document.body.innerHTML = ''
+})
+
+describe('probeComposerCaret', () => {
+  it('returns the textarea selection when the DOM is in sync with the draft', () => {
+    mountComposer('hello world', 5, 5)
+    expect(probeComposerCaret('hello world')).toEqual({ start: 5, end: 5 })
+  })
+
+  it('reports a live selection range, not just a collapsed caret', () => {
+    mountComposer('hello world', 6, 11)
+    expect(probeComposerCaret('hello world')).toEqual({ start: 6, end: 11 })
+  })
+
+  it('returns null when no composer is mounted', () => {
+    expect(document.querySelector('textarea')).toBeNull()
+    expect(probeComposerCaret('anything')).toBeNull()
+  })
+
+  it('returns null when the composer DOM value is out of sync with the store draft', () => {
+    mountComposer('hello', 0, 0)
+    expect(probeComposerCaret('hello changed on the server')).toBeNull()
+  })
+
+  it('returns null for a disabled composer', () => {
+    const input = mountComposer('hello', 2, 2)
+    input.disabled = true
+    expect(probeComposerCaret('hello')).toBeNull()
+  })
+
+  it('returns null for a read-only composer', () => {
+    const input = mountComposer('hello', 2, 2)
+    input.readOnly = true
+    expect(probeComposerCaret('hello')).toBeNull()
+  })
+
+  it('clamps out-of-range selections into the draft bounds', () => {
+    const input = mountComposer('hi', 0, 0)
+    // Direct property writes (jsdom does not enforce bounds like browsers).
+    input.selectionStart = 5
+    input.selectionEnd = 9
+    expect(probeComposerCaret('hi')).toEqual({ start: 2, end: 2 })
+  })
+})
+
+describe('insertAtCaret', () => {
+  it('appends at the end when the caret is unknown (pre-fix behavior)', () => {
+    expect(insertAtCaret('', 'X', null)).toBe('X')
+    expect(insertAtCaret('hello', 'X', null)).toBe('hello X')
+    expect(insertAtCaret('   ', 'X', null)).toBe('X')
+  })
+
+  it('inserts at the caret in the middle of a sentence with one space each side', () => {
+    expect(insertAtCaret('hello world', 'CODE', { start: 5, end: 5 })).toBe('hello CODE world')
+  })
+
+  it('only adds the separating spaces the neighbors actually need', () => {
+    expect(insertAtCaret('one two', 'CODE', { start: 3, end: 3 })).toBe('one CODE two')
+    // Doubled gap, caret right after the word: the leading space is added,
+    // the two after the caret stay untouched (like typing in the gap).
+    expect(insertAtCaret('one  two', 'CODE', { start: 3, end: 3 })).toBe('one CODE  two')
+    // Doubled gap, caret on the second space: neither side needs a new
+    // space, both originals flank the insertion.
+    expect(insertAtCaret('one  two', 'CODE', { start: 4, end: 4 })).toBe('one CODE two')
+    expect(insertAtCaret('one two ', 'CODE', { start: 8, end: 8 })).toBe('one two CODE')
+  })
+
+  it('inserts at the start without a leading space', () => {
+    expect(insertAtCaret('hello', 'CODE', { start: 0, end: 0 })).toBe('CODE hello')
+  })
+
+  it('inserts at the end with a single trailing space', () => {
+    expect(insertAtCaret('hello', 'CODE', { start: 5, end: 5 })).toBe('hello CODE')
+  })
+
+  it('replaces the live selection', () => {
+    expect(insertAtCaret('a little tale', 'CODE', { start: 2, end: 8 })).toBe('a CODE tale')
+  })
+
+  it('replaces a selection surrounded by words with single-space joins', () => {
+    expect(insertAtCaret('abc def ghi', 'CODE', { start: 4, end: 7 })).toBe('abc CODE ghi')
+  })
+
+  it('replaces a selection spanning the whole draft', () => {
+    expect(insertAtCaret('old', 'CODE', { start: 0, end: 3 })).toBe('CODE')
+  })
+
+  it('handles an empty draft with a resolved caret', () => {
+    expect(insertAtCaret('', 'CODE', { start: 0, end: 0 })).toBe('CODE')
+  })
+})
\ No newline at end of file