diff --git a/.github/workflows/gemini-invoke.yml b/.github/workflows/gemini-invoke.yml
index 11bc2c6..27649bc 100644
--- a/.github/workflows/gemini-invoke.yml
+++ b/.github/workflows/gemini-invoke.yml
@@ -44,8 +44,9 @@ jobs:
         id: 'run_gemini'
         uses: 'google-github-actions/run-gemini-cli@v0' # ratchet:exclude
         env:
-          TITLE: '${{ github.event.pull_request.title || github.event.issue.title }}'
-          DESCRIPTION: '${{ github.event.pull_request.body || github.event.issue.body }}'
+          # TITLE and DESCRIPTION intentionally omitted: passing raw GitHub event
+          # content as env vars is a prompt-injection vector. The agent should
+          # fetch PR/issue content via the GitHub API using ISSUE_NUMBER.
           EVENT_NAME: '${{ github.event_name }}'
           GITHUB_TOKEN: '${{ steps.mint_identity_token.outputs.token || secrets.GITHUB_TOKEN || github.token }}'
           IS_PULL_REQUEST: '${{ !!github.event.pull_request }}'
diff --git a/.github/workflows/gemini-review.yml b/.github/workflows/gemini-review.yml
index 4bd4470..a6ddbed 100644
--- a/.github/workflows/gemini-review.yml
+++ b/.github/workflows/gemini-review.yml
@@ -46,8 +46,8 @@ jobs:
         id: 'gemini_pr_review'
         env:
           GITHUB_TOKEN: '${{ steps.mint_identity_token.outputs.token || secrets.GITHUB_TOKEN || github.token }}'
-          ISSUE_TITLE: '${{ github.event.pull_request.title || github.event.issue.title }}'
-          ISSUE_BODY: '${{ github.event.pull_request.body || github.event.issue.body }}'
+          # ISSUE_TITLE and ISSUE_BODY intentionally omitted: prompt-injection vector.
+          # Agent must fetch content via GitHub API using PULL_REQUEST_NUMBER.
           PULL_REQUEST_NUMBER: '${{ github.event.pull_request.number || github.event.issue.number }}'
           REPOSITORY: '${{ github.repository }}'
           ADDITIONAL_CONTEXT: '${{ inputs.additional_context }}'
diff --git a/.github/workflows/release-cherry-pick.yml b/.github/workflows/release-cherry-pick.yml
index ac5e5c0..3daab1d 100644
--- a/.github/workflows/release-cherry-pick.yml
+++ b/.github/workflows/release-cherry-pick.yml
@@ -18,7 +18,7 @@ jobs:
   cherry-pick:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           ref: release/candidate
           fetch-depth: 0
diff --git a/.github/workflows/release-cut.yml b/.github/workflows/release-cut.yml
index 8dbed40..00d624c 100644
--- a/.github/workflows/release-cut.yml
+++ b/.github/workflows/release-cut.yml
@@ -18,7 +18,7 @@ jobs:
   cut-release:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           ref: ${{ inputs.commit_sha || 'main' }}
 
diff --git a/.github/workflows/release-finalize.yml b/.github/workflows/release-finalize.yml
index b9d6203..8214a02 100644
--- a/.github/workflows/release-finalize.yml
+++ b/.github/workflows/release-finalize.yml
@@ -29,7 +29,7 @@ jobs:
             echo "is_release_pr=false" >> $GITHUB_OUTPUT
           fi
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         if: steps.check.outputs.is_release_pr == 'true'
         with:
           ref: release/candidate
diff --git a/.github/workflows/release-please.yml b/.github/workflows/release-please.yml
index 791d84a..19a7eb5 100644
--- a/.github/workflows/release-please.yml
+++ b/.github/workflows/release-please.yml
@@ -30,7 +30,7 @@ jobs:
             echo "exists=false" >> $GITHUB_OUTPUT
           fi
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         if: steps.check.outputs.exists == 'true'
         with:
           ref: release/candidate
diff --git a/.github/workflows/release-publish.yml b/.github/workflows/release-publish.yml
index 95ee326..5293967 100644
--- a/.github/workflows/release-publish.yml
+++ b/.github/workflows/release-publish.yml
@@ -28,7 +28,7 @@ jobs:
           echo "version=$VERSION" >> $GITHUB_OUTPUT
           echo "Publishing version: $VERSION"
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
 
       - name: Install uv
         uses: astral-sh/setup-uv@v4
@@ -36,7 +36,7 @@ jobs:
           version: "latest"
 
       - name: Set up Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
 
diff --git a/.github/workflows/unit-tests.yaml b/.github/workflows/unit-tests.yaml
index e3769d5..0d2cbe7 100644
--- a/.github/workflows/unit-tests.yaml
+++ b/.github/workflows/unit-tests.yaml
@@ -16,10 +16,10 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.python-version }}