fix(slack): collect thread attachments across recent messages instead of only the newest

.changeset/slack-thread-attachment-lookback.md

@@ -0,0 +1,5 @@
+---
+"eve": patch
+---
+
+Fix the Slack thread attachment lookback only ever inspecting the newest non-bot message. When a user posted an image in a thread and then mentioned the agent in a text-only follow-up, the image was silently dropped and the model saw no file parts. The lookback now collects attachments from recent non-bot messages across the thread, newest first, capped at 10 file parts.

packages/eve/src/public/channels/slack/attachments.test.ts

@@ -345,6 +345,108 @@ describe("collectInboundFileParts", () => {
     expect((parts[0]!.data as URL).href).toBe("https://files.slack.com/a/b/from-user.csv");
   });
 
+  it("looks past a newer text-only message to find files earlier in the thread", async () => {
+    const refresh = vi.fn().mockResolvedValue(undefined);
+    const thread = makeSlackThread({
+      refresh,
+      recentMessages: [
+        {
+          isMe: false,
+          raw: {
+            files: [
+              {
+                id: "F500",
+                name: "earlier.png",
+                mimetype: "image/png",
+                url_private: "https://files.slack.com/a/b/earlier.png",
+              },
+            ],
+          },
+        },
+        { isMe: false, raw: {} },
+      ],
+    });
+
+    const parts = await collectInboundFileParts({
+      mention: emptyMention,
+      thread,
+      policy: DEFAULT_UPLOAD_POLICY,
+    });
+
+    expect(parts).toHaveLength(1);
+    expect((parts[0]!.data as URL).href).toBe("https://files.slack.com/a/b/earlier.png");
+  });
+
+  it("collects files from multiple thread messages, newest first", async () => {
+    const refresh = vi.fn().mockResolvedValue(undefined);
+    const thread = makeSlackThread({
+      refresh,
+      recentMessages: [
+        {
+          isMe: false,
+          raw: {
+            files: [
+              {
+                id: "F600",
+                mimetype: "text/csv",
+                url_private: "https://files.slack.com/a/b/older.csv",
+              },
+            ],
+          },
+        },
+        {
+          isMe: false,
+          raw: {
+            files: [
+              {
+                id: "F601",
+                mimetype: "image/png",
+                url_private: "https://files.slack.com/a/b/newer.png",
+              },
+            ],
+          },
+        },
+      ],
+    });
+
+    const parts = await collectInboundFileParts({
+      mention: emptyMention,
+      thread,
+      policy: DEFAULT_UPLOAD_POLICY,
+    });
+
+    expect(parts).toHaveLength(2);
+    expect((parts[0]!.data as URL).href).toBe("https://files.slack.com/a/b/newer.png");
+    expect((parts[1]!.data as URL).href).toBe("https://files.slack.com/a/b/older.csv");
+  });
+
+  it("caps thread-history collection at 10 file parts", async () => {
+    const refresh = vi.fn().mockResolvedValue(undefined);
+    const makeFiles = (prefix: string, count: number) =>
+      Array.from({ length: count }, (_, i) => ({
+        id: `${prefix}${i}`,
+        mimetype: "image/png",
+        url_private: `https://files.slack.com/a/b/${prefix}${i}.png`,
+      }));
+    const thread = makeSlackThread({
+      refresh,
+      recentMessages: [
+        { isMe: false, raw: { files: makeFiles("old", 6) } },
+        { isMe: false, raw: { files: makeFiles("new", 6) } },
+      ],
+    });
+
+    const parts = await collectInboundFileParts({
+      mention: emptyMention,
+      thread,
+      policy: DEFAULT_UPLOAD_POLICY,
+    });
+
+    expect(parts).toHaveLength(10);
+    expect((parts[0]!.data as URL).href).toBe("https://files.slack.com/a/b/new0.png");
+    expect((parts[9]!.data as URL).href).toBe("https://files.slack.com/a/b/old3.png");
+  });
+
   it.each([
     ["'disabled' literal", DISABLED_POLICY],
     ["maxBytes: 0", ZERO_BYTES_POLICY],

packages/eve/src/public/channels/slack/attachments.ts

@@ -66,17 +66,24 @@ function toSlackFilePart(attachment: SlackAttachment, index: number): FilePart |
   };
 }
 
+/**
+ * Upper bound on file parts collected from thread history for a single
+ * turn, keeping model input bounded on long, attachment-heavy threads.
+ */
+const THREAD_LOOKBACK_MAX_FILES = 10;
+
 /**
  * Collects file parts for an inbound mention.
  *
  * Prefers attachments on the triggering mention (the common case: user
  * uploads a file and mentions the bot in the same message). When the
  * mention has none, refreshes the thread via {@link SlackThread.refresh}
- * and picks the latest non-bot message's attachments — covering the
- * case where a user dropped a file in the thread first, then mentioned
- * the bot in a follow-up. Any error during refresh is logged and treated
- * as "no attachments" so the text portion of the mention still gets
- * delivered.
+ * and collects attachments from non-bot messages across the thread,
+ * newest first, capped at {@link THREAD_LOOKBACK_MAX_FILES} — covering
+ * the case where a user dropped a file in the thread first, then
+ * mentioned the bot in a follow-up. Any error during refresh is logged
+ * and treated as "no attachments" so the text portion of the mention
+ * still gets delivered.
  *
  * Skips the thread-history lookback when the policy disables uploads,
  * since the refresh can't surface anything we'd deliver.
@@ -100,16 +107,16 @@ export async function collectInboundFileParts(input: {
   }
 
   const recent = input.thread.recentMessages;
-  for (let i = recent.length - 1; i >= 0; i -= 1) {
+  const collected: FilePart[] = [];
+  for (let i = recent.length - 1; i >= 0 && collected.length < THREAD_LOOKBACK_MAX_FILES; i -= 1) {
     const candidate = recent[i];
     if (!candidate || candidate.isMe) continue;
     const raw = candidate.raw as { files?: readonly Record<string, unknown>[] } | undefined;
     const attachments = extractAttachmentsFromRaw(raw?.files);
     const parts = collectSlackFileParts(attachments, input.policy);
-    if (parts.length > 0) return parts;
-    return [];
+    collected.push(...parts.slice(0, THREAD_LOOKBACK_MAX_FILES - collected.length));
   }
-  return [];
+  return collected;
 }
 
 function extractAttachmentsFromRaw(