diff --git a/mcp-server/CHANGELOG.md b/mcp-server/CHANGELOG.md
index 79d1a6bf..faa7b4a4 100644
--- a/mcp-server/CHANGELOG.md
+++ b/mcp-server/CHANGELOG.md
@@ -5,6 +5,29 @@ All notable changes to `loopctl-mcp-server` are documented here.
 Format: [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 
+## 2.74.0 — 2026-08-12 (one search command, three response shapes)
+
+### Added
+
+- **`knowledge_search` takes `format`: `results` (default), `stubs`, or `bodies`.** These are
+  response SHAPES of one search, not different searches — the server dispatches `stubs` to the
+  same `progressive_index/3` and `bodies` to the same `get_context/3` that
+  `knowledge_progressive_index` and `knowledge_context` call.
+
+  **Nothing is retired.** Both sibling tools remain registered and work exactly as before;
+  they are now siblings on one path rather than separate doors to choose between.
+
+  Why it is worth having at all: an agent's choice of entrypoint is unobservable, so it
+  confounds any measurement of the ranking behind it — you cannot separate an algorithm's
+  effect from a choice you cannot see. A parameter is a variable the server controls; a tool
+  choice is a confounder it does not. This is the precondition for judging a ranking change
+  from observed behaviour.
+
+  Two refusals, deliberately not silent: `stubs` and `bodies` REQUIRE a query (they are
+  relevance shapes; there is no stub rendering of an enumeration page), and an unknown value
+  is a 400 rather than a quiet downgrade to `results`. A downgrade would answer a different
+  question than the one asked, and an agent could read the result as an empty corpus.
+
 ## 2.73.0 — 2026-08-12 (one spelling for the search parameter, plus a body window and prefix-tolerant ids)
 
 ### Changed
diff --git a/mcp-server/index.js b/mcp-server/index.js
index 38ce1f69..98370ceb 100755
--- a/mcp-server/index.js
+++ b/mcp-server/index.js
@@ -1497,9 +1497,16 @@ async function knowledgeFacets({
   return toContent(result);
 }
 
-async function knowledgeSearch({ q, project_id, story_id, category, tags, match, mode, limit, offset }) {
+async function knowledgeSearch({ q, project_id, story_id, category, tags, match, mode, format, limit, offset }) {
   const params = new URLSearchParams();
   if (q != null && q !== "") params.set("q", q);
+  // `format` is the SHAPE of the response, not a different search (#678). The server
+  // dispatches `stubs` to the same progressive_index/3 and `bodies` to the same
+  // get_context/3 that knowledge_progressive_index and knowledge_context call, so those
+  // tools remain and are not retired — they are now siblings on one path rather than
+  // separate doors an agent has to choose between. That choice was unobservable and
+  // therefore confounded any measurement of the ranking behind it.
+  if (format) params.set("format", format);
   if (project_id) params.set("project_id", project_id);
   if (story_id) params.set("story_id", story_id);
   if (category) params.set("category", category);
@@ -4616,6 +4623,21 @@ const TOOLS = [
           enum: ["keyword", "semantic", "combined"],
           description: "Optional: search mode (keyword, semantic, or combined).",
         },
+        format: {
+          type: "string",
+          enum: ["results", "stubs", "bodies"],
+          description:
+            "Optional: the SHAPE of the response, not a different search. 'results' " +
+            "(default) is ranked results plus snippets and is the only shape that " +
+            "supports cursor pagination. 'stubs' returns capped stubs with one hop of hub " +
+            "enrichment — use it to survey a broad topic without pulling bodies into " +
+            "context, then knowledge_progressive_drill into a chosen stub. 'bodies' " +
+            "returns full article bodies plus linked references for one deep read. " +
+            "'stubs' and 'bodies' REQUIRE a query; sending either without one is a 400, " +
+            "as is an unknown value (it is never silently downgraded to 'results'). These " +
+            "dispatch to exactly the same code knowledge_progressive_index and " +
+            "knowledge_context call, which both remain available.",
+        },
         limit: {
           type: "integer",
           description: "Optional: maximum number of results to return.",
diff --git a/mcp-server/package.json b/mcp-server/package.json
index 92bb59fb..77391cd5 100644
--- a/mcp-server/package.json
+++ b/mcp-server/package.json
@@ -1,6 +1,6 @@
 {
   "name": "loopctl-mcp-server",
-  "version": "2.73.0",
+  "version": "2.74.0",
   "description": "MCP server for loopctl \u2014 structural trust for AI development loops",
   "type": "module",
   "main": "index.js",
diff --git a/mcp-server/test/search_format_param.test.js b/mcp-server/test/search_format_param.test.js
new file mode 100644
index 00000000..47ff82f4
--- /dev/null
+++ b/mcp-server/test/search_format_param.test.js
@@ -0,0 +1,70 @@
+/**
+ * `knowledge_search` gained a `format` parameter (loopctl#678): one command, three response
+ * shapes, dispatching to the same progressive_index/3 and get_context/3 the sibling tools
+ * call. The siblings are NOT retired.
+ *
+ * Asserted against the index.js SOURCE rather than through a re-implemented helper. The
+ * other suites here re-implement handler bodies by design (index.js has top-level await and
+ * exports nothing), but a re-implementation cannot catch the failure that matters for a
+ * pass-through parameter: the schema advertising a field the request builder never forwards.
+ * Reading the source is the only check that stays true when index.js changes.
+ */
+
+import { test, describe } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import path from "node:path";
+
+const here = path.dirname(fileURLToPath(import.meta.url));
+const source = readFileSync(path.join(here, "..", "index.js"), "utf8");
+
+describe("knowledge_search format parameter", () => {
+  test("the request builder actually forwards it", () => {
+    assert.match(
+      source,
+      /async function knowledgeSearch\(\{[^}]*\bformat\b[^}]*\}\)/,
+      "knowledgeSearch must destructure `format`",
+    );
+    assert.match(
+      source,
+      /if \(format\) params\.set\("format", format\);/,
+      "knowledgeSearch must forward `format` as a query param",
+    );
+  });
+
+  test("the schema advertises exactly the shapes the server accepts", () => {
+    const block = source.slice(source.indexOf('name: "knowledge_search"'));
+    const formatProp = block.slice(block.indexOf("format: {"), block.indexOf("limit: {"));
+
+    assert.ok(formatProp.includes("format: {"), "knowledge_search must declare `format`");
+    for (const shape of ["results", "stubs", "bodies"]) {
+      assert.ok(formatProp.includes(`"${shape}"`), `format enum must include ${shape}`);
+    }
+  });
+
+  test("the description tells an agent the two ways it is refused", () => {
+    const block = source.slice(source.indexOf('name: "knowledge_search"'));
+    const formatProp = block.slice(block.indexOf("format: {"), block.indexOf("limit: {"));
+
+    // Both are 400s on the server, and an agent that expects a silent downgrade to
+    // `results` would misread an error as an empty corpus.
+    assert.match(formatProp, /REQUIRE a query/, "must say stubs/bodies need a query");
+    assert.match(formatProp, /never silently downgraded/, "must say an unknown value 400s");
+  });
+
+  test("it does not claim the sibling tools were removed", () => {
+    const block = source.slice(source.indexOf('name: "knowledge_search"'));
+    const formatProp = block.slice(block.indexOf("format: {"), block.indexOf("limit: {"));
+
+    assert.match(formatProp, /both remain available/);
+    assert.ok(
+      source.includes('name: "knowledge_progressive_index"'),
+      "knowledge_progressive_index must still be registered",
+    );
+    assert.ok(
+      source.includes('name: "knowledge_context"'),
+      "knowledge_context must still be registered",
+    );
+  });
+});