fix(codex): reserve the label's share of a qualified command row

A child's label is raw provider text and was spliced into the command
row unbounded, then the pair clipped to the description cap. A label at
or past that cap clipped the command away entirely, leaving a row of
kind 'command' that named an agent and showed no command - the failure
qualification exists to remove, inverted. The same clip could also cut a
surrogate pair, which boundSubagentField already guards against on the
agent row two lines away.

Give the label a reserved share and clip it the way the agent row does.

src/main/codex/codex-background-command-tracker.ts

@@ -10,9 +10,31 @@ const MAX_DESCRIPTION_CHARS = 512
 
 type Command = { threadId: string; task: AgentSessionBackgroundTask; bytes: number }
 
-/** Stays within the retained bound, so read-time qualification cannot outgrow admission. */
+/** The label's reserved share of the description. Reserved, not merely capped:
+ *  a label free to spend the whole budget clips away the command it qualifies,
+ *  leaving a command row naming an agent and no command — the failure this
+ *  qualification exists to remove, in the other direction. `bytes` is counted
+ *  before qualification, so this share is also what a published row may exceed
+ *  the admitted count by. */
+const MAX_LABEL_CHARS = 96
+
+/** Clipped the way `boundSubagentField` clips the same provider string on the
+ *  agent row: never mid surrogate pair, since a lone surrogate is lossy through
+ *  any non-JSON UTF-8 hop. No ordinal, because the row's identity is its `id`. */
+function boundLabel(label: string): string {
+  if (label.length <= MAX_LABEL_CHARS) {
+    return label
+  }
+  const keep = MAX_LABEL_CHARS - 1
+  const last = label.charCodeAt(keep - 1)
+  const end = last >= 0xd800 && last <= 0xdbff ? keep - 1 : keep
+  return `${label.slice(0, end)}…`
+}
+
+/** Resolved on read, and capped at the bound the admitted description already respects. */
 function qualifiedDescription(label: string, description: string | undefined): string {
-  return (description ? `${label} — ${description}` : label).slice(0, MAX_DESCRIPTION_CHARS)
+  const name = boundLabel(label)
+  return (description ? `${name} — ${description}` : name).slice(0, MAX_DESCRIPTION_CHARS)
 }
 
 export class CodexBackgroundCommandTracker {

src/main/codex/codex-background-task-tracker.test.ts

@@ -22,7 +22,8 @@ function turn(
 function activity(
   kind = 'started',
   parentTurn = PARENT_TURN,
-  child = CHILD
+  child = CHILD,
+  name = 'count_a'
 ): CodexBackgroundTaskEvent {
   return {
     method: 'item/started',
@@ -35,7 +36,7 @@ function activity(
         id: `activity-${kind}`,
         kind,
         agentThreadId: child,
-        agentPath: '/root/count_a'
+        agentPath: `/root/${name}`
       }
     }
   }
@@ -261,6 +262,32 @@ describe('CodexBackgroundTaskTracker command integration', () => {
     })
   })
 
+  it('keeps the command visible under a label that would otherwise fill the row', () => {
+    const tracker = new CodexBackgroundTaskTracker(PRIMARY)
+    tracker.observe(turn('turn/started', PRIMARY, PARENT_TURN))
+    tracker.observe(turn('turn/started', CHILD, CHILD_TURN))
+    tracker.observe(activity('started', PARENT_TURN, CHILD, 'L'.repeat(600)))
+    tracker.observe(command(CHILD))
+    tracker.observe(turn('turn/completed', PRIMARY, PARENT_TURN))
+    tracker.observe(turn('turn/completed', CHILD, CHILD_TURN))
+    const description = tracker.state?.tasks?.[0]?.description
+    expect(description).toContain('sleep 90')
+    expect(description).toBe(`${'L'.repeat(95)}… — sleep 90`)
+  })
+
+  it('never cuts a label mid surrogate pair', () => {
+    const tracker = new CodexBackgroundTaskTracker(PRIMARY)
+    tracker.observe(turn('turn/started', PRIMARY, PARENT_TURN))
+    tracker.observe(turn('turn/started', CHILD, CHILD_TURN))
+    tracker.observe(activity('started', PARENT_TURN, CHILD, `${'L'.repeat(94)}\u{1F600}bad`))
+    tracker.observe(command(CHILD))
+    tracker.observe(turn('turn/completed', PRIMARY, PARENT_TURN))
+    tracker.observe(turn('turn/completed', CHILD, CHILD_TURN))
+    const description = tracker.state?.tasks?.[0]?.description ?? ''
+    expect(description.isWellFormed()).toBe(true)
+    expect(description).toBe(`${'L'.repeat(94)}… — sleep 90`)
+  })
+
   it('names a child shell whose label only arrives after the command', () => {
     const tracker = new CodexBackgroundTaskTracker(PRIMARY)
     tracker.observe(turn('turn/started', PRIMARY, PARENT_TURN))