diff --git a/src/main/ai-vault-search/session-search-child-service.ts b/src/main/ai-vault-search/session-search-child-service.ts
index 92ad066d417..7859d4e612e 100644
--- a/src/main/ai-vault-search/session-search-child-service.ts
+++ b/src/main/ai-vault-search/session-search-child-service.ts
@@ -27,7 +27,9 @@ export function createChildSessionSearchService(
     search: async (request, hostScope) => {
       try {
         return await calls.search(request, hostScope)
-      } catch {
+      } catch (error) {
+        // The child's own search errors land here too; without this they read only as "not ready".
+        console.warn('[ai-vault-search] search failed', error)
         return { kind: 'unavailable', reason: 'not-ready' }
       }
     },
diff --git a/src/main/ai-vault-search/session-search-row-filter.test.ts b/src/main/ai-vault-search/session-search-row-filter.test.ts
index 1cec0a528f9..680b7801714 100644
--- a/src/main/ai-vault-search/session-search-row-filter.test.ts
+++ b/src/main/ai-vault-search/session-search-row-filter.test.ts
@@ -59,6 +59,7 @@ describe('a cwd scope is the sidebar key, or anything below it', () => {
     ['/work/app-other', '/work/app', false],
     ['/work/a_b/src', '/work/a_b', true],
     ['/work/axb/src', '/work/a_b', false],
+    ['/work/lone\ud800/src', '/work/lone\ud800', true],
     // Roots: `/` is the one key that is already a separator, which is where a
     // range bound is easiest to get wrong. A Windows key is not under POSIX `/`.
     ['/', '/', true],
@@ -143,5 +144,13 @@ it('plans a cwd scope as a seek on sessions_cwd_key, never a scan', async () =>
 
   expect(plan.join(' | ')).toContain('sessions_cwd_key')
   expect(plan.some((detail) => detail.startsWith('SEARCH'))).toBe(true)
-  expect(plan.some((detail) => detail.startsWith('SCAN sessions'))).toBe(false)
+  expect(plan.some((detail) => /^SCAN (sessions|scoped)\b/.test(detail))).toBe(false)
+})
+
+it('matches under a thousand-plus scopes, past where an OR chain exceeds SQLite expression depth', async () => {
+  const db = await openIndex()
+  addSession(db, 1, '/lanes/lane-1199/src')
+  addSession(db, 2, '/elsewhere')
+  const scopePaths = Array.from({ length: 1_200 }, (_, index) => `/lanes/lane-${index}`)
+  expect(selected(db, { scopePaths })).toEqual([1])
 })
diff --git a/src/main/ai-vault-search/session-search-row-filter.ts b/src/main/ai-vault-search/session-search-row-filter.ts
index 4f5b6106e7d..a268a06ef8b 100644
--- a/src/main/ai-vault-search/session-search-row-filter.ts
+++ b/src/main/ai-vault-search/session-search-row-filter.ts
@@ -49,39 +49,44 @@ export function sessionRowFilter(
     filter.values.push(filters.since)
   }
   if (filters.scopePaths && filters.scopePaths.length > 0) {
-    // Several scopes mean any of them; every other narrowing is ANDed on.
-    const present = filters.scopePaths
-      .map((scope) => scopeCondition(filter, scope))
-      .filter((condition) => condition !== null)
-    // Every scope unkeyable still means a scope, so it narrows to nothing;
-    // pushing no condition would widen the search to every session instead.
-    filter.conditions.push(present.length > 0 ? `(${present.join(' OR ')})` : '0 = 1')
+    // Any scope matches; one that cannot be keyed matches nothing, and all-unkeyable must not widen to every session.
+    const keys = filters.scopePaths.map(cwdKey).filter((key) => key !== null)
+    if (keys.length === 0) {
+      filter.conditions.push('0 = 1')
+    } else {
+      filter.conditions.push(SCOPE_CONDITION)
+      filter.values.push(JSON.stringify(keys.map(scopeRange)))
+    }
   }
   return filter
 }
 
-/** A scope the caller could not key is a scope nothing is inside of. */
-function scopeCondition(filter: SessionRowFilter, scope: string): string | null {
-  const key = cwdKey(scope)
-  return key === null ? null : insideCondition(filter, key)
-}
-
 /**
- * `key` itself, or anything below it. Why a half-open range and not
- * `substr(key, 1, length(?)) = ?`: only `>=`/`<` can seek `sessions_cwd_key`;
- * the substr form scans it. The bound is the child prefix with its last byte
- * incremented, so it stops at the end of that prefix and nowhere else. The two
- * arms cannot merge: one range over the bare key would also swallow a sibling
- * like `/work/app-other`. No wildcards, so `%`/`_` in a folder name are literal.
+ * `key` itself, or anything below it. One JSON parameter, not an OR per scope:
+ * ~500 OR arms exceed SQLite's expression depth of 1000 and the search throws.
+ *
+ * Why a half-open range and not `substr(key, 1, length(?)) = ?`: only `>=`/`<`
+ * can seek `sessions_cwd_key`; the substr form scans it. The bound is the child
+ * prefix with its last byte incremented, so it stops at the end of that prefix
+ * and nowhere else. The two arms cannot merge: one range over the bare key would
+ * also swallow a sibling like `/work/app-other`. No wildcards, so `%`/`_` in a
+ * folder name are literal.
  *
  * The filesystem root is the one key that already ends in a separator, and
  * appending a second one would bound the range at `//`, which sorts below every
  * real child; `cwdKey` keeps it as `/` for exactly this reason.
  */
-function insideCondition(filter: SessionRowFilter, key: string): string {
+const SCOPE_CONDITION = `id IN (
+  SELECT scoped.id FROM json_each(?) AS scope JOIN sessions AS scoped
+    ON scoped.${CWD} = scope.value ->> 0
+    OR (scoped.${CWD} >= scope.value ->> 1 AND scoped.${CWD} < scope.value ->> 2)
+)`
+
+function scopeRange(scopeKey: string): [string, string, string] {
+  // A bound key stores a lone surrogate as U+FFFD; JSON would decode it to other bytes.
+  const key = scopeKey.toWellFormed()
   const children = key.endsWith('/') ? key : `${key}/`
-  filter.values.push(key, children, nextAfterPrefix(children))
-  return `(${CWD} = ? OR (${CWD} >= ? AND ${CWD} < ?))`
+  return [key, children, nextAfterPrefix(children)]
 }
 
 /** The first string that sorts after every string starting with `prefix`. */