diff --git a/.gitea/workflows/ci.yaml b/.gitea/workflows/ci.yaml
index ad4761a..748c38d 100644
--- a/.gitea/workflows/ci.yaml
+++ b/.gitea/workflows/ci.yaml
@@ -14,6 +14,13 @@ jobs:
           node-version: 22
       - name: Validate repository documentation
         run: test -f README.md && test -f AGENTS.md && test -f docs/versioning.md
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+      - name: Validate restored-session schema and negative cases
+        run: |
+          python -m pip install jsonschema==4.26.0
+          python tests/session_contract.py
       - name: Validate JSON contracts and fixtures
         run: |
           node --input-type=module <<'NODE'
diff --git a/README.md b/README.md
index 4dff980..132c4e1 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,11 @@ request and response envelopes; bearer values in fixtures are synthetic only.
 Twitch OAuth link and completion response envelopes are also versioned here;
 fixtures contain no real credentials or tokens.
 
+`GET /api/v1/auth/session` returns `authenticated: true` and the current
+`must_replace_credentials` flag from the administrator account. Restoring a
+session must not bypass first-run setup. Older servers omit this flag; clients
+must not interpret an absent flag as completed credential replacement.
+
 The shared boundary vocabulary includes the ordered permission levels in
 `contracts/v1/permissions.json` and the client/server compatibility result in
 `contracts/v1/version-negotiation.json`. Server-owned state is delivered as
@@ -49,4 +54,3 @@ only synthetic Twitch IDs and literal response templates.
 
 Typed command arguments use `bot-command-argument-definition.json` and remain
 literal validated data.
-
diff --git a/contracts/v1/auth-session-response.json b/contracts/v1/auth-session-response.json
index 4f4ab2d..eea1273 100644
--- a/contracts/v1/auth-session-response.json
+++ b/contracts/v1/auth-session-response.json
@@ -4,8 +4,9 @@
   "title": "Trixie Session Response",
   "type": "object",
   "additionalProperties": false,
-  "required": ["authenticated"],
+  "required": ["authenticated", "must_replace_credentials"],
   "properties": {
-    "authenticated": { "const": true }
+    "authenticated": { "const": true },
+    "must_replace_credentials": { "type": "boolean" }
   }
 }
diff --git a/docs/contract-testing.md b/docs/contract-testing.md
index 9aa0033..38bedbf 100644
--- a/docs/contract-testing.md
+++ b/docs/contract-testing.md
@@ -16,3 +16,11 @@ than in a URL query parameter. The server closes the connection when the frame
 is missing, malformed, or invalid, and sends `connection.ready` only after
 successful validation.
 
+The restored-session contract has Draft 2020-12 validation for both credential
+replacement states, missing fields, wrong types, and unexpected properties:
+
+```sh
+uv run --with jsonschema==4.26.0 python tests/session_contract.py
+```
+
+This isolated validation dependency is tooling only, not an application dependency.
diff --git a/fixtures/v1/auth-session.authenticated.json b/fixtures/v1/auth-session.authenticated.json
index aab331f..ad510d5 100644
--- a/fixtures/v1/auth-session.authenticated.json
+++ b/fixtures/v1/auth-session.authenticated.json
@@ -1,3 +1,4 @@
 {
-  "authenticated": true
+  "authenticated": true,
+  "must_replace_credentials": false
 }
diff --git a/fixtures/v1/auth-session.bootstrap.json b/fixtures/v1/auth-session.bootstrap.json
new file mode 100644
index 0000000..e901e5c
--- /dev/null
+++ b/fixtures/v1/auth-session.bootstrap.json
@@ -0,0 +1,4 @@
+{
+  "authenticated": true,
+  "must_replace_credentials": true
+}
diff --git a/tests/session_contract.py b/tests/session_contract.py
new file mode 100644
index 0000000..023fa98
--- /dev/null
+++ b/tests/session_contract.py
@@ -0,0 +1,24 @@
+"""Validate restored-session fixtures and rejection cases against Draft 2020-12."""
+
+import json
+from pathlib import Path
+
+from jsonschema import Draft202012Validator
+
+root = Path(__file__).resolve().parents[1]
+schema = json.loads((root / "contracts/v1/auth-session-response.json").read_text())
+Draft202012Validator.check_schema(schema)
+validator = Draft202012Validator(schema)
+
+for name in ["auth-session.authenticated.json", "auth-session.bootstrap.json"]:
+    validator.validate(json.loads((root / "fixtures/v1" / name).read_text()))
+
+for invalid in [
+    {"authenticated": True},
+    {"authenticated": False, "must_replace_credentials": False},
+    {"authenticated": True, "must_replace_credentials": "false"},
+    {"authenticated": True, "must_replace_credentials": False, "unexpected": True},
+]:
+    assert not validator.is_valid(invalid), "Invalid session response was accepted"
+
+print("Session schema: two valid fixtures and four rejection cases passed")