diff --git a/improvements.md b/improvements.md
index ba9c30a..3267944 100644
--- a/improvements.md
+++ b/improvements.md
@@ -68,7 +68,7 @@ you which stack PR closes the row.**
 | 14  | Multi-file push undocumented                             | Discoverability                                    | None       | RESOLVED 2026-04-30 (Stack A)     |
 | 15  | Scoped push rewrites entire state file                   | Pre-existing drift sweeps into focused commits     | #4         | Open (Stack J planned)            |
 | 16  | No CLI runner for simulation suites                      | Engine pushes them, can't run them                 | None       | Open (Stack E planned)            |
-| 17  | State file key-order churn produces noisy diffs          | Reorderings hide real changes                      | None       | Open (Stack B planned)            |
+| 17  | State file key-order churn produces noisy diffs          | Reorderings hide real changes                      | None       | RESOLVED 2026-04-30 (Stack B)     |
 | 18  | Structured-output `name` capped at 40 chars (no warning) | Push fails partway after partial application       | None       | Open (Stack D planned)            |
 | 19  | No `maxTokens` floor warning for tool-using assistants   | `maxTokens: 1` bricks the assistant silently       | None       | Open (Stack D planned)            |
 | 20  | Prompt vocabulary leaks into TTS                         | `Reason.` becomes verbal contaminant               | None       | Open (Stack D heuristic planned)  |
diff --git a/src/state-serialize.ts b/src/state-serialize.ts
new file mode 100644
index 0000000..67975d4
--- /dev/null
+++ b/src/state-serialize.ts
@@ -0,0 +1,48 @@
+// Pure serialization helpers for the state file (and snapshot files).
+//
+// Kept config-free so tests can import without triggering the CLI argument
+// parser in `config.ts` (which `process.exit(1)`s when no env is supplied).
+
+// JSON.stringify replacer that emits object keys in alphabetical order at
+// every nesting level. Without this, the state file diff includes pure
+// reorderings every time a resource map gets rebuilt from multiple sources
+// (push, pull, bootstrap) — about half the diff lines are insertion-order
+// churn rather than semantic change. Reviewers stop reading state diffs
+// closely as a result, which defeats the point of versioning the file.
+//
+// Arrays are returned as-is so existing array order (e.g. squad members,
+// tool destinations) is preserved.
+export function sortedKeysReplacer(_key: string, value: unknown): unknown {
+  if (value === null || typeof value !== "object" || Array.isArray(value)) {
+    return value;
+  }
+  const sorted: Record<string, unknown> = {};
+  for (const k of Object.keys(value as Record<string, unknown>).sort()) {
+    sorted[k] = (value as Record<string, unknown>)[k];
+  }
+  return sorted;
+}
+
+// Canonicalize a value: sort object keys at every level, drop null/undefined
+// leaves recursively, leave array order intact. Produces a stable shape
+// regardless of insertion order or transient nullish leaves the API may
+// emit. Used by Stack F (content hashes) and Stack G (drift detection) —
+// kept here so the helpers stay co-located.
+export function canonicalize(value: unknown): unknown {
+  if (value === null || value === undefined) return undefined;
+  if (Array.isArray(value)) {
+    const out: unknown[] = [];
+    for (const item of value) {
+      const c = canonicalize(item);
+      if (c !== undefined) out.push(c);
+    }
+    return out;
+  }
+  if (typeof value !== "object") return value;
+  const sorted: Record<string, unknown> = {};
+  for (const k of Object.keys(value as Record<string, unknown>).sort()) {
+    const c = canonicalize((value as Record<string, unknown>)[k]);
+    if (c !== undefined) sorted[k] = c;
+  }
+  return sorted;
+}
diff --git a/src/state.ts b/src/state.ts
index 152bd54..f822e92 100644
--- a/src/state.ts
+++ b/src/state.ts
@@ -1,8 +1,14 @@
 import { existsSync, readFileSync } from "fs";
 import { rename, writeFile } from "fs/promises";
 import { STATE_FILE_PATH, VAPI_ENV } from "./config.ts";
+import { sortedKeysReplacer } from "./state-serialize.ts";
 import type { StateFile } from "./types.ts";
 
+// Re-export the pure helper so callers can pull it from `state.ts` (same
+// import line as loadState/saveState) without forcing the config-laden
+// module on test code that just wants the serializer.
+export { sortedKeysReplacer } from "./state-serialize.ts";
+
 // ─────────────────────────────────────────────────────────────────────────────
 // State Management
 // ─────────────────────────────────────────────────────────────────────────────
@@ -57,8 +63,16 @@ export async function saveState(state: StateFile): Promise<void> {
   // A crash or SIGINT mid-write leaves the original state intact rather than
   // truncating it. A truncated state file would silently wipe all UUID
   // mappings on the next load.
+  // sortedKeysReplacer enforces deterministic key ordering across every
+  // nested object so two semantically-equal state objects (with different
+  // insertion orders from push/pull/bootstrap merges) always serialize
+  // byte-identically. Without this, ~half of the state-file diff is pure
+  // reordering, which trains reviewers to skim past it.
   const tmpPath = `${STATE_FILE_PATH}.tmp`;
-  await writeFile(tmpPath, JSON.stringify(state, null, 2) + "\n");
+  await writeFile(
+    tmpPath,
+    JSON.stringify(state, sortedKeysReplacer, 2) + "\n",
+  );
   await rename(tmpPath, STATE_FILE_PATH);
   console.log(`💾 Saved state file: ${STATE_FILE_PATH}`);
 }
diff --git a/tests/state-key-order.test.ts b/tests/state-key-order.test.ts
new file mode 100644
index 0000000..d791fd0
--- /dev/null
+++ b/tests/state-key-order.test.ts
@@ -0,0 +1,96 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import { sortedKeysReplacer } from "../src/state-serialize.ts";
+
+// Stack B regression test — pin deterministic key ordering on state file
+// serialization. Two semantically equal state objects with different
+// insertion orders MUST serialize byte-identically. Without this, the state
+// file accumulates pure-reordering diffs that hide real changes.
+
+test("sortedKeysReplacer emits top-level keys alphabetically", () => {
+  const insertedABC = { c: 3, a: 1, b: 2 };
+  const insertedCBA = { a: 1, b: 2, c: 3 };
+
+  const serializedABC = JSON.stringify(insertedABC, sortedKeysReplacer, 2);
+  const serializedCBA = JSON.stringify(insertedCBA, sortedKeysReplacer, 2);
+
+  assert.equal(serializedABC, serializedCBA);
+  assert.equal(
+    serializedABC,
+    `{
+  "a": 1,
+  "b": 2,
+  "c": 3
+}`,
+  );
+});
+
+test("sortedKeysReplacer recursively sorts nested objects", () => {
+  const a = {
+    assistants: { z: "uuid-z", a: "uuid-a" },
+    tools: { y: "uuid-y", b: "uuid-b" },
+  };
+  const b = {
+    tools: { b: "uuid-b", y: "uuid-y" },
+    assistants: { a: "uuid-a", z: "uuid-z" },
+  };
+
+  assert.equal(
+    JSON.stringify(a, sortedKeysReplacer, 2),
+    JSON.stringify(b, sortedKeysReplacer, 2),
+  );
+});
+
+test("sortedKeysReplacer leaves array order intact", () => {
+  // Array order is semantic for resource lists like `assistant_ids` —
+  // sorting them would corrupt squad member ordering, tool destination
+  // priority, etc. The replacer MUST NOT reorder arrays.
+  const obj = { tags: ["zebra", "apple", "mango"] };
+  const result = JSON.parse(JSON.stringify(obj, sortedKeysReplacer));
+  assert.deepEqual(result.tags, ["zebra", "apple", "mango"]);
+});
+
+test("sortedKeysReplacer handles deeply nested mixed structures", () => {
+  const insertion1 = {
+    z: { y: { x: 1, w: 2 }, v: [{ b: 1, a: 2 }, { d: 1, c: 2 }] },
+    a: 0,
+  };
+  const insertion2 = {
+    a: 0,
+    z: { v: [{ b: 1, a: 2 }, { d: 1, c: 2 }], y: { w: 2, x: 1 } },
+  };
+
+  assert.equal(
+    JSON.stringify(insertion1, sortedKeysReplacer, 2),
+    JSON.stringify(insertion2, sortedKeysReplacer, 2),
+  );
+});
+
+test("sortedKeysReplacer preserves null and primitive values", () => {
+  const obj = {
+    voicemailMessage: null,
+    name: "test",
+    count: 42,
+    enabled: true,
+    nothing: undefined, // JSON.stringify drops undefined naturally
+  };
+  const serialized = JSON.stringify(obj, sortedKeysReplacer, 2);
+  const parsed = JSON.parse(serialized);
+  assert.equal(parsed.voicemailMessage, null);
+  assert.equal(parsed.name, "test");
+  assert.equal(parsed.count, 42);
+  assert.equal(parsed.enabled, true);
+  assert.equal("nothing" in parsed, false);
+});
+
+test("sortedKeysReplacer is stable: serializing twice yields identical output", () => {
+  const state = {
+    credentials: { c: "1", a: "2" },
+    assistants: { z: "3", b: "4" },
+    tools: { y: "5", x: "6" },
+  };
+
+  const first = JSON.stringify(state, sortedKeysReplacer, 2);
+  const second = JSON.stringify(JSON.parse(first), sortedKeysReplacer, 2);
+  assert.equal(first, second);
+});