diff --git a/packages/junior/src/chat/slack/channel.ts b/packages/junior/src/chat/slack/channel.ts
index a05ef1e72..6835d396a 100644
--- a/packages/junior/src/chat/slack/channel.ts
+++ b/packages/junior/src/chat/slack/channel.ts
@@ -32,6 +32,11 @@ export interface SlackThreadReply {
   type?: string;
   files?: SlackFileRef[];
   attachments?: unknown[];
+  reactions?: Array<{
+    name?: string;
+    count?: number;
+    users?: string[];
+  }>;
 }
 
 /** List channel history using Slack-native, pre-validated timestamp bounds. */
diff --git a/packages/junior/src/chat/slack/tools/channel-list-messages.ts b/packages/junior/src/chat/slack/tools/channel-list-messages.ts
index 090a7a93f..c3aa4d5d0 100644
--- a/packages/junior/src/chat/slack/tools/channel-list-messages.ts
+++ b/packages/junior/src/chat/slack/tools/channel-list-messages.ts
@@ -79,34 +79,45 @@ export function createSlackChannelListMessagesTool(context: SlackToolContext) {
       readOnlyHint: true,
     },
     inputSchema: z.object({
-      channel_id: slackChannelRefParam.optional(),
+      channel_id: slackChannelRefParam.nullable().optional(),
       limit: z.coerce
         .number()
         .int()
         .min(1)
         .max(1000)
         .describe("Maximum number of messages to return across pages.")
+        .nullable()
         .optional(),
       cursor: z
         .string()
         .min(1)
-        .describe("Optional cursor to continue from a prior call.")
+        .describe(
+          "Cursor from `next_cursor` in a prior result. Use null or omit it for the first page; never invent a cursor.",
+        )
+        .nullable()
         .optional(),
       oldest: slackTimestampParam(
         "Oldest message timestamp (Slack ts) for range filtering.",
-      ).optional(),
+      )
+        .nullable()
+        .optional(),
       latest: slackTimestampParam(
         "Latest message timestamp (Slack ts) for range filtering.",
-      ).optional(),
+      )
+        .nullable()
+        .optional(),
       inclusive: booleanInput(
         "Whether oldest/latest bounds should be inclusive.",
-      ).optional(),
+      )
+        .nullable()
+        .optional(),
       max_pages: z.coerce
         .number()
         .int()
         .min(1)
         .max(10)
         .describe("Maximum number of API pages to traverse in a single call.")
+        .nullable()
         .optional(),
     }),
     outputSchema: juniorToolOutputSchema,
@@ -121,7 +132,7 @@ export function createSlackChannelListMessagesTool(context: SlackToolContext) {
     }) => {
       const target = await resolveOptionalSlackChannelRef({
         field: "channel_id",
-        value: channel_id,
+        value: channel_id ?? undefined,
         defaultChannelId: context.destinationChannelId,
         teamId: context.teamId,
       });
@@ -141,7 +152,7 @@ export function createSlackChannelListMessagesTool(context: SlackToolContext) {
 
       const normalizedOldest = normalizeRangeTimestamp(
         "oldest",
-        oldest,
+        oldest ?? undefined,
         targetChannelId,
       );
       if (!normalizedOldest.ok) {
@@ -149,7 +160,7 @@ export function createSlackChannelListMessagesTool(context: SlackToolContext) {
       }
       const normalizedLatest = normalizeRangeTimestamp(
         "latest",
-        latest,
+        latest ?? undefined,
         targetChannelId,
       );
       if (!normalizedLatest.ok) {
@@ -160,11 +171,11 @@ export function createSlackChannelListMessagesTool(context: SlackToolContext) {
         listChannelMessages({
           channelId: targetChannelId,
           limit: limit ?? 100,
-          cursor,
+          cursor: cursor ?? undefined,
           oldest: normalizedOldest.value,
           latest: normalizedLatest.value,
-          inclusive,
-          maxPages: max_pages,
+          inclusive: inclusive ?? undefined,
+          maxPages: max_pages ?? undefined,
         });
 
       let result: Awaited<ReturnType<typeof listChannelMessages>> | undefined;
diff --git a/packages/junior/src/chat/slack/tools/thread-read.ts b/packages/junior/src/chat/slack/tools/thread-read.ts
index 7cb3c712d..de9c9ef5d 100644
--- a/packages/junior/src/chat/slack/tools/thread-read.ts
+++ b/packages/junior/src/chat/slack/tools/thread-read.ts
@@ -69,6 +69,15 @@ function sanitizeMessage(
     subtype: msg.subtype,
     bot_id: msg.bot_id,
     type: msg.type,
+    ...(msg.reactions?.length
+      ? {
+          reactions: msg.reactions.map((reaction) => ({
+            name: reaction.name,
+            count: reaction.count,
+            users: reaction.users,
+          })),
+        }
+      : undefined),
     ...(attachmentText ? { attachment_text: attachmentText } : undefined),
     ...(files.length
       ? {
@@ -119,7 +128,7 @@ export function createSlackThreadReadTool(
 ) {
   return zodTool({
     description:
-      "Read a Slack thread from a shared archive URL or explicit channel + timestamp. Works for the current conversation and public channels.",
+      "Read a Slack thread, including message reaction users, from a shared archive URL or explicit channel + timestamp. Works for the current conversation and public channels.",
     annotations: {
       destructiveHint: false,
       idempotentHint: true,
@@ -127,17 +136,25 @@ export function createSlackThreadReadTool(
       readOnlyHint: true,
     },
     inputSchema: z.object({
-      url: z.string().min(1).describe("Slack message archive URL.").optional(),
-      channel_id: slackChannelRefParam.optional(),
+      url: z
+        .string()
+        .min(1)
+        .describe("Slack message archive URL.")
+        .nullable()
+        .optional(),
+      channel_id: slackChannelRefParam.nullable().optional(),
       ts: slackTimestampParam(
         "Slack message timestamp. May be the thread root or any message in the thread.",
-      ).optional(),
+      )
+        .nullable()
+        .optional(),
       limit: z.coerce
         .number()
         .int()
         .min(1)
         .max(1000)
         .describe("Maximum number of thread messages to fetch.")
+        .nullable()
         .optional(),
       max_pages: z.coerce
         .number()
@@ -145,6 +162,7 @@ export function createSlackThreadReadTool(
         .min(1)
         .max(10)
         .describe("Maximum number of Slack API pages to traverse.")
+        .nullable()
         .optional(),
     }),
     outputSchema: juniorToolOutputSchema,
@@ -197,7 +215,7 @@ export function createSlackThreadReadTool(
           channelId,
           threadTs: lookupTs,
           limit: limit ?? 1000,
-          maxPages: max_pages,
+          maxPages: max_pages ?? undefined,
         });
 
       let replies: SlackThreadReply[] | undefined;
diff --git a/packages/junior/tests/integration/slack-channel-tools.test.ts b/packages/junior/tests/integration/slack-channel-tools.test.ts
index 3d9d29957..0f5958ffa 100644
--- a/packages/junior/tests/integration/slack-channel-tools.test.ts
+++ b/packages/junior/tests/integration/slack-channel-tools.test.ts
@@ -193,9 +193,12 @@ describe("slack channel tools", () => {
     );
 
     const result = await executeTool(tool, {
+      channel_id: null,
       limit: 150,
+      cursor: null,
       oldest: "1690000000.000",
       latest: "1710000000",
+      inclusive: null,
       max_pages: 3,
     });
 
diff --git a/packages/junior/tests/integration/slack-thread-read.test.ts b/packages/junior/tests/integration/slack-thread-read.test.ts
index 4557b25c3..ac4776a68 100644
--- a/packages/junior/tests/integration/slack-thread-read.test.ts
+++ b/packages/junior/tests/integration/slack-thread-read.test.ts
@@ -171,6 +171,13 @@ describe("slackThreadRead", () => {
             thread_ts: "1700000000.500000",
             user: "U1",
             text: "standalone message",
+            reactions: [
+              {
+                name: "raised_hands",
+                count: 2,
+                users: ["U2", "U3"],
+              },
+            ],
           },
         ],
       }),
@@ -180,13 +187,27 @@ describe("slackThreadRead", () => {
     const result = await executeTool(tool, {
       channel_id: "C0MANUAL",
       ts: "1700000000.500000",
+      url: null,
+      limit: null,
+      max_pages: null,
     });
 
     expect(result).toMatchObject({
       channel_id: "C0MANUAL",
       count: 1,
+      messages: [
+        {
+          text: "standalone message",
+          reactions: [
+            {
+              name: "raised_hands",
+              count: 2,
+              users: ["U2", "U3"],
+            },
+          ],
+        },
+      ],
     });
-    expect(result.messages[0].text).toBe("standalone message");
   });
 
   it("allows reading a private channel when it matches the current channel", async () => {