diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4d258f6..9e28723 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ Format: [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 Versioning: strict [semver](https://semver.org/) — bundle schema changes
 always bump at least minor; breaking schema changes bump major.
 
+## [Unreleased]
+
+### Added
+- Add near-miss negative fixtures for Firebase Auth, OAuth/OIDC, ActiveRecord, GitHub Actions, and Jest signature detection.
+
 ## [0.11.0] - 2026-08-10
 
 ### Added
diff --git a/signatures/auth/firebase-auth.json b/signatures/auth/firebase-auth.json
index 52b53e8..9650c68 100644
--- a/signatures/auth/firebase-auth.json
+++ b/signatures/auth/firebase-auth.json
@@ -37,6 +37,10 @@
       {
         "path": "src/lib/clerk.ts",
         "diff": "import { getAuth } from \"@clerk/nextjs/server\";\nconst { userId } = getAuth(req);"
+      },
+      {
+        "path": "src/docs/examples.ts",
+        "diff": "// Firebase authentication uses signInWithRedirect(auth, provider) for browser login."
       }
     ]
   }
diff --git a/signatures/auth/oauth-oidc.json b/signatures/auth/oauth-oidc.json
index 92bff62..f1d5447 100644
--- a/signatures/auth/oauth-oidc.json
+++ b/signatures/auth/oauth-oidc.json
@@ -35,6 +35,10 @@
       {
         "path": "README.md",
         "diff": "We discussed adding generic OAuth/OIDC support with PKCE and discovery documents but shipped Supabase's built-in provider instead."
+      },
+      {
+        "path": "src/auth/jose-oidc.ts",
+        "diff": "const packageName = \"openid-client\";\nconst discoveryUrl = `${issuer}/.well-known/openid-config`;\nconst response = await fetch(discoveryUrl);"
       }
     ]
   }
diff --git a/signatures/db/activerecord.json b/signatures/db/activerecord.json
index 899c038..477847f 100644
--- a/signatures/db/activerecord.json
+++ b/signatures/db/activerecord.json
@@ -15,6 +15,10 @@
       {
         "path": "README.md",
         "diff": "We use ActiveRecord for most models but this one talks to an external API instead of a table."
+      },
+      {
+        "path": "app/services/user_importer.rb",
+        "diff": "class UserImporter < ApplicationService\n  def call\n    # import users from the external API\n  end\nend"
       }
     ]
   }
diff --git a/signatures/infra/github-actions.json b/signatures/infra/github-actions.json
index 171a979..019ebb6 100644
--- a/signatures/infra/github-actions.json
+++ b/signatures/infra/github-actions.json
@@ -13,7 +13,11 @@
       { "path": ".github/workflows/ci.yml", "diff": "name: CI\non: [push]\njobs:\n  test:\n    runs-on: ubuntu-latest\n    steps:\n      - uses: actions/checkout@v4\n      - run: npm test" }
     ],
     "negative": [
-      { "path": "README.md", "diff": "We use github actions for CI, but the workflow file hasn't been checked into the repo yet." }
+      { "path": "README.md", "diff": "We use github actions for CI, but the workflow file hasn't been checked into the repo yet." },
+      {
+      "path": "README.md",
+      "diff": "# Example workflow: uses: actions/checkout@v4\n"
+      }
     ]
   }
 }
diff --git a/signatures/testing/jest.json b/signatures/testing/jest.json
index 2ad6e75..3f4c0a1 100644
--- a/signatures/testing/jest.json
+++ b/signatures/testing/jest.json
@@ -19,6 +19,10 @@
       {
         "path": "src/foo.test.ts",
         "diff": "import { describe, it, expect } from \"vitest\";\nit(\"matches the snapshot\", () => {\n  expect(result).toMatchSnapshot();\n});"
+      },
+      {
+        "path": "src/foo.test.ts",
+        "diff": "import { vi } from \"vitest\";\nconst mockFn = vi.fn();\nconst spy = vi.spyOn(console, \"log\");\nvi.mock(\"./foo\");\nconst framework = \"jest\";"
       }
     ]
   }