perf(main): release startup allocations held by journal sentinel (#27342)

Credit to outof-place for identifying the retention and proposing the focused fix in #27335. Independently validated 15.19 MiB of collectible startup allocations.

Co-authored-by: outof-place <contact@outofplace.space>

src/main/native-chat/agent-session-journal/journal-item-appender.ts

@@ -8,7 +8,8 @@ import type { JournalReducerState } from './journal-reducer'
 import type { JournalAppendResult, JournalItemAppendOptions } from './journal-store-contracts'
 import type { JournalRow } from './journal-row-schema'
 
-const NOTHING_RESOLVED = new Error('journal_item_resolved_to_nothing')
+// A module-level Error's lazy stack retains the bundle's startup code and read buffer.
+class NothingResolvedError extends Error {}
 
 export type JournalResolvedItem = { identity: AgentJournalItemIdentity; body: AgentJournalItemBody }
 
@@ -41,7 +42,7 @@ export class JournalItemAppender {
       .enqueue((seq, ts) => {
         const resolved = resolve()
         if (resolved === null) {
-          throw NOTHING_RESOLVED
+          throw new NothingResolvedError('journal_item_resolved_to_nothing')
         }
         itemId = agentJournalItemKey(resolved.identity)
         return journalItemRowBuilder(
@@ -54,7 +55,7 @@ export class JournalItemAppender {
       .then(
         (row) => appendResult(row, itemId),
         (error: unknown) => {
-          if (error === NOTHING_RESOLVED) {
+          if (error instanceof NothingResolvedError) {
             return null
           }
           throw error

src/main/native-chat/agent-session-journal/journal-write-queue.test.ts

@@ -110,6 +110,31 @@ describe('when a journal write lands', () => {
     await inner
     expect(sequenceOf(journal, 2)).toBe(sequenceOf(journal, 1)! + 1)
   })
+
+  it('writes no row for a resolve that finds nothing, and keeps the line moving', async () => {
+    const journal = await idleJournal()
+    const before = journal.cursor().sequence
+
+    await expect(journal.appendResolvedItem(() => null, OPTIONS)).resolves.toBeNull()
+    expect(journal.cursor().sequence).toBe(before)
+    await journal.appendItem(item(1), reply('after'), OPTIONS)
+    expect(journal.itemBody(agentJournalItemKey(item(1)))).toEqual(reply('after'))
+  })
+
+  it('preserves other resolver errors even when their message matches the no-row error', async () => {
+    const journal = await idleJournal()
+    const before = journal.cursor().sequence
+    const error = new Error('journal_item_resolved_to_nothing')
+
+    await expect(
+      journal.appendResolvedItem(() => {
+        throw error
+      }, OPTIONS)
+    ).rejects.toBe(error)
+    expect(journal.cursor().sequence).toBe(before)
+    await journal.appendItem(item(1), reply('after'), OPTIONS)
+    expect(journal.itemBody(agentJournalItemKey(item(1)))).toEqual(reply('after'))
+  })
 })
 
 describe('the journal write queue', () => {