📏 fix: Let activityCharLimit Reach Tool Inputs

Round-fifteen review: `activityCharLimit` is documented as the
per-entry truncation for tool input AND output, but `buildPrompt`
hard-coded inputs at 200 characters — so raising the setting could
never surface a distinguishing path, query, or operation that appears
past the first 200 characters of a long argument. Inputs now truncate
at the configured limit alongside outputs; the 200-char constant
remains only for the intent line (renamed INTENT_CHAR_LIMIT to match).
Config fidelity pinned in runtime.spec: a 400-char argument survives a
450 limit and truncates under a 50 limit.

The round's other finding is the fifth restatement of the documented
edited+reconnect index-space limitation, answered on-thread with the
prior four cross-references.

packages/api/src/agents/activityLabels/__tests__/runtime.spec.ts

@@ -139,6 +139,42 @@ describe('buildPrompt', () => {
     expect(line).toContain('x'.repeat(100));
   });
 
+  /** `activityCharLimit` is documented as the per-entry limit for tool input
+   *  AND output — a hard-coded input cap would make the setting unable to
+   *  reach a distinguishing path or query past the first 200 characters. */
+  it('applies the configured charLimit to tool inputs, not a hard-coded cap', () => {
+    const longQuery = 'q'.repeat(400);
+    const prompt = buildPrompt(
+      [
+        {
+          toolName: 'search',
+          toolInput: { query: longQuery },
+          toolUseId: 'a',
+          status: 'success',
+          toolOutput: 'ok',
+        },
+      ],
+      450,
+    );
+    /** 400-char argument survives intact under a 450 limit (the old 200-char
+     *  cap would have cut it), while a tighter limit still truncates. */
+    expect(prompt).toContain(longQuery);
+    const tight = buildPrompt(
+      [
+        {
+          toolName: 'search',
+          toolInput: { query: longQuery },
+          toolUseId: 'a',
+          status: 'success',
+          toolOutput: 'ok',
+        },
+      ],
+      50,
+    );
+    expect(tight).not.toContain('q'.repeat(60));
+    expect(tight).toContain('…');
+  });
+
   it('serializes small structured values exactly like JSON.stringify', () => {
     const toolInput = { q: 'docs', filters: { lang: 'en', page: 2 }, ids: [1, 2] };
     const prompt = buildPrompt(

packages/api/src/agents/activityLabels/runtime.ts

@@ -167,7 +167,11 @@ export interface ActivityLabelHookOptions {
 
 const DEFAULT_MAX_PER_RUN = 20;
 const DEFAULT_CHAR_LIMIT = 600;
-const INPUT_CHAR_LIMIT = 200;
+/** Intent-line truncation only. Tool inputs and outputs both truncate at the
+ *  configured `activityCharLimit` — the schema documents it as the per-entry
+ *  limit for BOTH, so a hard-coded input cap would make the setting unable to
+ *  reach a distinguishing path or query past the first 200 characters. */
+const INTENT_CHAR_LIMIT = 200;
 const SUMMARY_TIMEOUT_MS = 12_000;
 /** Hard bound on the PERSISTED label. The instruction asks for 4–9 words, but
  *  a model that ignores it — or is steered by injection through untrusted
@@ -331,7 +335,7 @@ export function buildPrompt(
   const sections: string[] = [instruction ?? ACTIVITY_INSTRUCTION];
   if (context?.lastAssistantText) {
     sections.push(
-      `Intent (assistant's last message): ${truncate(context.lastAssistantText, INPUT_CHAR_LIMIT)}`,
+      `Intent (assistant's last message): ${truncate(context.lastAssistantText, INTENT_CHAR_LIMIT)}`,
     );
   }
   if (context?.thinkingExcerpts?.length) {
@@ -344,7 +348,7 @@ export function buildPrompt(
     );
   }
   const lines = entries.map((entry) => {
-    const input = truncate(stringifyUnknown(entry.toolInput, INPUT_CHAR_LIMIT), INPUT_CHAR_LIMIT);
+    const input = truncate(stringifyUnknown(entry.toolInput, charLimit), charLimit);
     const outcome =
       entry.status === 'error'
         ? `ERROR: ${truncate(entry.error ?? 'unknown error', charLimit)}`