diff --git a/README.md b/README.md
index 8aa37f8..4f895fa 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,8 @@ Add to your Claude Code config (`~/.claude.json` or project `.mcp.json`):
       "args": ["/absolute/path/to/agent-bridge/dist/index.js"],
       "env": {
         "AGENT_BRIDGE_URL": "https://your-project.supabase.co",
-        "AGENT_BRIDGE_KEY": "your-anon-key-here"
+        "AGENT_BRIDGE_KEY": "your-anon-key-here",
+        "AGENT_BRIDGE_AGENT": "codex"
       }
     }
   }
@@ -98,7 +99,7 @@ Restart your MCP client. Three tools become available: `post_context`, `get_cont
 
 | Parameter | Type | Required | Description |
 |-----------|------|----------|-------------|
-| `source` | string | yes | Agent name (e.g. `"claude-code"`) |
+| `source` | string | yes | Agent name. When `AGENT_BRIDGE_AGENT` is set, this must match it. |
 | `category` | string | yes | Entry type (see [Categories](#categories)) |
 | `content` | string | yes | The context message |
 | `priority` | string | no | `info` (default), `high`, `urgent` |
@@ -155,6 +156,8 @@ cp bin/agent-bridge ~/.openclaw/scripts/agent-bridge
 
 The CLI reads credentials from `~/.agent-bridge/config` (created in step 3).
 
+When `AGENT_BRIDGE_AGENT` is set for the MCP server or CLI, posts with a different `source` are rejected. This prevents a wrapped runtime from writing rows labelled as another agent after atrib has already signed the original tool arguments.
+
 ### CLI Reference
 
 ```bash
diff --git a/bin/agent-bridge b/bin/agent-bridge
index 5467401..1f96c4d 100755
--- a/bin/agent-bridge
+++ b/bin/agent-bridge
@@ -95,6 +95,15 @@ cmd_post() {
     esac
   done
 
+  if [[ -n "${AGENT_BRIDGE_AGENT:-}" ]]; then
+    if [[ -z "$source" ]]; then
+      source="$AGENT_BRIDGE_AGENT"
+    elif [[ "$source" != "$AGENT_BRIDGE_AGENT" ]]; then
+      echo "Error: --source must match AGENT_BRIDGE_AGENT ($AGENT_BRIDGE_AGENT); got $source" >&2
+      exit 1
+    fi
+  fi
+
   if [[ -z "$source" || -z "$category" || -z "$content" ]]; then
     echo "Error: --source, --category, and content are required" >&2
     exit 1
diff --git a/src/server.ts b/src/server.ts
index 071fa0f..6e322c4 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -25,6 +25,7 @@ import {
   filterContextRows,
   mergeEnvelopeMetadata,
 } from "./message-envelope.js";
+import { resolvePostSource } from "./source-identity.js";
 
 const headers = {
   apikey: SUPABASE_KEY,
@@ -67,7 +68,8 @@ export async function startServer() {
           properties: {
             source: {
               type: "string",
-              description: 'Agent posting this entry (e.g. "claude-code", "sido")',
+              description:
+                "Agent posting this entry. Must match AGENT_BRIDGE_AGENT when configured.",
             },
             category: {
               type: "string",
@@ -236,10 +238,20 @@ export async function startServer() {
 
     switch (name) {
       case "post_context": {
+        let source: string | undefined;
+        try {
+          source = resolvePostSource(args?.source, process.env.AGENT_BRIDGE_AGENT);
+        } catch (e) {
+          throw new McpError(
+            ErrorCode.InvalidParams,
+            e instanceof Error ? e.message : "source identity mismatch"
+          );
+        }
+        const postArgs = { ...(args ?? {}), source };
         const receiptId = normalizeReceiptId(args?.atrib_receipt_id);
-        const envelope = buildMessageEnvelope(args, receiptId);
+        const envelope = buildMessageEnvelope(postArgs, receiptId);
         const body: Record<string, unknown> = {
-          source: args?.source,
+          source,
           category: args?.category,
           content: args?.content,
           priority: args?.priority || "info",
diff --git a/src/source-identity.ts b/src/source-identity.ts
new file mode 100644
index 0000000..fa6b797
--- /dev/null
+++ b/src/source-identity.ts
@@ -0,0 +1,21 @@
+function normalizeSource(value: unknown): string | undefined {
+  if (typeof value !== "string") return undefined;
+  const trimmed = value.trim();
+  return trimmed ? trimmed : undefined;
+}
+
+export function resolvePostSource(
+  requestedSource: unknown,
+  configuredAgent: unknown
+): string | undefined {
+  const source = normalizeSource(requestedSource);
+  const configured = normalizeSource(configuredAgent);
+
+  if (source && configured && source !== configured) {
+    throw new Error(
+      `source must match AGENT_BRIDGE_AGENT (${configured}); got ${source}`
+    );
+  }
+
+  return source ?? configured;
+}
diff --git a/test/source_identity.test.ts b/test/source_identity.test.ts
new file mode 100644
index 0000000..a671403
--- /dev/null
+++ b/test/source_identity.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+import { resolvePostSource } from "../src/source-identity.js";
+
+describe("resolvePostSource", () => {
+  it("accepts a source that matches the configured agent", () => {
+    expect(resolvePostSource("codex", "codex")).toBe("codex");
+  });
+
+  it("falls back to the configured agent when no source is passed", () => {
+    expect(resolvePostSource(undefined, "claude-code")).toBe("claude-code");
+  });
+
+  it("keeps legacy source arguments when no configured agent exists", () => {
+    expect(resolvePostSource("sido", undefined)).toBe("sido");
+  });
+
+  it("rejects source labels that do not match the configured agent", () => {
+    expect(() => resolvePostSource("claude-code", "codex")).toThrow(
+      "source must match AGENT_BRIDGE_AGENT (codex); got claude-code"
+    );
+  });
+});