diff --git a/.github/actions/splice-wf-run/action.yml b/.github/actions/splice-wf-run/action.yml
index b73d09b..11a6b5f 100644
--- a/.github/actions/splice-wf-run/action.yml
+++ b/.github/actions/splice-wf-run/action.yml
@@ -5,6 +5,10 @@ inputs:
   source_workflow:
     description: Name of the source workflow that emitted the bridge artifact
     required: true
+  bridge_override_json:
+    description: Internal test-only JSON object used instead of consuming the bridge artifact; not part of the supported public API
+    required: false
+    default: ''
   allow_pr_author:
     description: Whether to always allow the PR author to trigger splice-bot
     required: false
@@ -90,7 +94,8 @@ runs:
         echo "branch-token source: ${{ steps.token_mode.outputs.branch_token_source }}"
 
     - name: Consume bridge artifact
-      id: bridge
+      if: inputs.bridge_override_json == ''
+      id: bridge_consume
       uses: leanprover-community/privilege-escalation-bridge/consume@v1
       with:
         token: ${{ inputs.token || github.token }}
@@ -113,6 +118,88 @@ runs:
           committer=outputs.committer
           author=outputs.author
 
+    - name: Load bridge override
+      if: inputs.bridge_override_json != ''
+      id: bridge_override
+      shell: bash
+      env:
+        BRIDGE_OVERRIDE_JSON: ${{ inputs.bridge_override_json }}
+      run: |
+        set -euo pipefail
+
+        ruby <<'RUBY'
+        require 'json'
+
+        raw = ENV.fetch('BRIDGE_OVERRIDE_JSON', '')
+        output_path = ENV.fetch('GITHUB_OUTPUT')
+        data = JSON.parse(raw)
+
+        unless data.is_a?(Hash)
+          warn 'bridge_override_json must be a JSON object.'
+          exit 1
+        end
+
+        keys = %w[
+          pr_number
+          review_comment_id
+          file_path
+          commenter_login
+          pr_author_login
+          base_ref
+          base_repo
+          head_repo
+          head_sha
+          head_ref
+          head_label
+          committer
+          author
+        ]
+
+        File.open(output_path, 'a') do |f|
+          keys.each do |key|
+            value = data[key]
+            next if value.nil?
+            f.puts("#{key}=#{value}")
+          end
+        end
+        RUBY
+
+    - name: Resolve bridge data
+      id: bridge
+      shell: bash
+      env:
+        PR_NUMBER: ${{ steps.bridge_override.outputs.pr_number || steps.bridge_consume.outputs.pr_number }}
+        REVIEW_COMMENT_ID: ${{ steps.bridge_override.outputs.review_comment_id || steps.bridge_consume.outputs.review_comment_id }}
+        FILE_PATH: ${{ steps.bridge_override.outputs.file_path || steps.bridge_consume.outputs.file_path }}
+        COMMENTER_LOGIN: ${{ steps.bridge_override.outputs.commenter_login || steps.bridge_consume.outputs.commenter_login }}
+        PR_AUTHOR_LOGIN: ${{ steps.bridge_override.outputs.pr_author_login || steps.bridge_consume.outputs.pr_author_login }}
+        BASE_REF: ${{ steps.bridge_override.outputs.base_ref || steps.bridge_consume.outputs.base_ref }}
+        BASE_REPO: ${{ steps.bridge_override.outputs.base_repo || steps.bridge_consume.outputs.base_repo }}
+        HEAD_REPO: ${{ steps.bridge_override.outputs.head_repo || steps.bridge_consume.outputs.head_repo }}
+        HEAD_SHA: ${{ steps.bridge_override.outputs.head_sha || steps.bridge_consume.outputs.head_sha }}
+        HEAD_REF: ${{ steps.bridge_override.outputs.head_ref || steps.bridge_consume.outputs.head_ref }}
+        HEAD_LABEL: ${{ steps.bridge_override.outputs.head_label || steps.bridge_consume.outputs.head_label }}
+        COMMITTER: ${{ steps.bridge_override.outputs.committer || steps.bridge_consume.outputs.committer }}
+        AUTHOR: ${{ steps.bridge_override.outputs.author || steps.bridge_consume.outputs.author }}
+      run: |
+        set -euo pipefail
+
+        {
+          echo "pr_number=${PR_NUMBER}"
+          echo "review_comment_id=${REVIEW_COMMENT_ID}"
+          echo "file_path=${FILE_PATH}"
+          echo "commenter_login=${COMMENTER_LOGIN}"
+          echo "pr_author_login=${PR_AUTHOR_LOGIN}"
+          echo "base_ref=${BASE_REF}"
+          echo "base_repo=${BASE_REPO}"
+          echo "head_repo=${HEAD_REPO}"
+          echo "head_sha=${HEAD_SHA}"
+          echo "head_ref=${HEAD_REF}"
+          echo "head_label=${HEAD_LABEL}"
+          echo "committer=${COMMITTER}"
+          echo "author=${AUTHOR}"
+        } >> "$GITHUB_OUTPUT"
+
     - name: Authorize commenter
       if: steps.bridge.outputs.file_path != ''
       id: authorize_commenter
diff --git a/.github/workflows/act_smoke.yaml b/.github/workflows/act_smoke.yaml
new file mode 100644
index 0000000..6c947ae
--- /dev/null
+++ b/.github/workflows/act_smoke.yaml
@@ -0,0 +1,35 @@
+name: Act Smoke Tests
+
+on:
+  pull_request:
+    paths:
+      - ".github/workflows/*.yml"
+      - ".github/workflows/*.yaml"
+      - ".github/actions/**/*.yml"
+      - ".github/actions/**/*.yaml"
+      - "tests/actions/**"
+  workflow_dispatch:
+
+jobs:
+  act-smoke:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Install act
+        shell: bash
+        run: |
+          set -euo pipefail
+          curl --silent --show-error --location \
+            https://raw.githubusercontent.com/nektos/act/master/install.sh \
+            | sudo bash -s -- -b /usr/local/bin
+
+      - name: Run act smoke suite
+        shell: bash
+        env:
+          DOCKER_AUTH_CONFIG: '{}'
+          GITHUB_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          tests/actions/run_act_smoke.sh
diff --git a/.github/workflows/splice.yaml b/.github/workflows/splice.yaml
index 1ae67db..cb643fe 100644
--- a/.github/workflows/splice.yaml
+++ b/.github/workflows/splice.yaml
@@ -22,6 +22,11 @@ on:
         required: false
         type: string
         default: '${{ github.event.pull_request.user.login }} <${{ github.event.pull_request.user.id }}+${{ github.event.pull_request.user.login }}@users.noreply.github.com>'
+      emit_bridge_artifact:
+        description: Whether to emit the bridge artifact; useful to disable in local smoke tests
+        required: false
+        type: boolean
+        default: true
 
 permissions: {}
 
@@ -33,6 +38,7 @@ jobs:
       - name: Verify caller event is pull_request_review_comment
         uses: actions/github-script@ed597411d8f924073f98dfc5c65a23a2325f34cd # v8.0.0
         with:
+          github-token: ${{ github.token }}
           script: |
             const eventName = context.eventName;
             const hasReviewCommentPayload = !!(context.payload?.comment && context.payload?.pull_request);
@@ -53,21 +59,28 @@ jobs:
           # Pass the reusable input down to the script and emit it as an output named base_ref
           BASE_REF_INPUT: ${{ inputs.base_ref }}
         with:
+          github-token: ${{ github.token }}
           script: |
             // NOTE: In actions/github-script, `core`, `github`, and `context` are provided globally.
             const comment = context.payload?.comment;
             const pr = context.payload?.pull_request;
             const body = comment?.body || "";
+            const triggerLine = body
+              .split(/\r?\n/)
+              .find((line) => /^splice-bot\b/i.test(line));
 
             core.info(`Comment body:\n---\n${body}\n---`);
 
             // Start-of-line match across lines; no leading whitespace allowed
-            if (!/^splice-bot\b/im.test(body)) {
+            if (!triggerLine) {
               core.info("No `splice-bot` found at the start of a line, skipping.");
               core.setOutput("skip", "true");
               return;
             }
 
+            const triggerKeyword = triggerLine.replace(/^splice-bot\b/i, "").trim().split(/\s+/)[0] || "";
+            core.info(`Trigger keyword: ${triggerKeyword || "(none)"}`);
+
             const path = comment?.path;
             if (!path) {
               core.info("This review comment is not on a file diff (no .path). Nothing to do.");
@@ -106,21 +119,24 @@ jobs:
             core.setOutput("skip", "false");
             // IMPORTANT: base_ref now comes from the reusable workflow input (default master)
             core.setOutput("base_ref", baseRefFromInput);
+            core.setOutput("trigger_keyword", triggerKeyword);
 
-      - if: ${{ steps.extract.outputs.skip != 'true' }}
+      - if: ${{ steps.extract.outputs.skip != 'true' && inputs.emit_bridge_artifact }}
         name: Prepare bridge outputs
         run: |
           jq -n \
             --arg base_ref "${{ steps.extract.outputs.base_ref }}" \
+            --arg trigger_keyword "${{ steps.extract.outputs.trigger_keyword }}" \
             --arg committer "${{ inputs.committer }}" \
             --arg author "${{ inputs.author }}" \
             '{
               base_ref: $base_ref,
+              trigger_keyword: $trigger_keyword,
               committer: $committer,
               author: $author,
             }' > bridge-outputs.json
 
-      - if: ${{ steps.extract.outputs.skip != 'true' }}
+      - if: ${{ steps.extract.outputs.skip != 'true' && inputs.emit_bridge_artifact }}
         name: Emit bridge artifact
         uses: leanprover-community/privilege-escalation-bridge/emit@v1
         with:
diff --git a/.github/workflows/workflow_lint.yaml b/.github/workflows/workflow_lint.yaml
index 7427a60..ec6e515 100644
--- a/.github/workflows/workflow_lint.yaml
+++ b/.github/workflows/workflow_lint.yaml
@@ -5,6 +5,8 @@ on:
     paths:
       - ".github/workflows/*.yml"
       - ".github/workflows/*.yaml"
+      - ".github/actions/**/*.yml"
+      - ".github/actions/**/*.yaml"
   workflow_dispatch:
 
 jobs:
@@ -15,4 +17,4 @@ jobs:
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
       - name: Run actionlint
-        uses: raven-actions/actionlint@e01d1ea33dd6a5ed517d95b4c0c357560ac6f518 # v2.1.1
+        uses: raven-actions/actionlint@205b530c5d9fa8f44ae9ed59f341a0db994aa6f8 # v2.1.2
diff --git a/README.md b/README.md
index 3dbd547..5beda9b 100644
--- a/README.md
+++ b/README.md
@@ -122,6 +122,51 @@ jobs:
           # branch_token: ${{ secrets.SPLICE_BOT_FORK_TOKEN }}
 ```
 
+## Local `act` smoke tests
+
+You can run the lightweight workflow smoke tests locally with [`act`](https://github.com/nektos/act).
+These tests exercise the reusable trigger workflow against canned review-comment payloads and intentionally skip bridge-artifact emission.
+The composite-action smoke harness uses the internal test-only `bridge_override_json` input; that input exists only for local/CI testing and is not part of the supported public API.
+
+Prerequisites:
+
+- `act` installed locally
+- Docker running
+- `GITHUB_TOKEN` available if the workflow under test needs it, for example:
+  `export GITHUB_TOKEN="$(gh auth token)"`
+
+Run all local `act` smoke tests:
+
+```bash
+tests/actions/run_act_smoke.sh
+```
+
+That script auto-discovers all reusable-workflow event fixtures under `tests/actions/events/` and then runs the composite-action smoke harness.
+If `GITHUB_TOKEN` is set in the environment, the script passes it through to `act` as a secret.
+
+You can also run individual harnesses directly.
+
+Example commands:
+
+```bash
+act \
+  --workflows tests/actions/workflows/splice_harness.yaml \
+  --eventpath tests/actions/events/pr-review-comment-basic.json \
+  pull_request_review_comment
+```
+
+```bash
+act \
+  --workflows tests/actions/workflows/splice_harness.yaml \
+  --eventpath tests/actions/events/pr-review-comment-keyword.json \
+  pull_request_review_comment
+```
+
+The canned event payloads live under `tests/actions/events/`.
+The CI workflow that runs the same smoke harness is `.github/workflows/act_smoke.yaml`.
+The reusable trigger harness lives at `tests/actions/workflows/splice_harness.yaml`.
+There is also a composite-action harness at `tests/actions/workflows/splice_action_harness.yaml` for deterministic non-network failure cases.
+
 ## GitHub App token minting in caller job
 
 ```yaml
@@ -238,6 +283,7 @@ Permission mapping references:
 | Name | Type | Required | Default | Description |
 | ---- | ---- | -------- | ------- | ----------- |
 | `source_workflow` | string | Yes | - | Name of the source workflow that emitted the bridge artifact. |
+| `bridge_override_json` | string | No | `''` | Internal test-only override used by the local/CI `act` harness instead of consuming the bridge artifact. Do not rely on this in normal workflow usage; it is not part of the supported public API. |
 | `allow_pr_author` | boolean | No | `true` | Always allow PR author to trigger. |
 | `min_repo_permission` | string | No | `anyone` | Minimum permission threshold: `anyone`, `triage`, `write`. |
 | `allowed_teams` | string | No | `''` | Comma/newline-separated team allowlist (`team-slug` or `org/team-slug`). |
@@ -249,6 +295,7 @@ Permission mapping references:
 | `branch_token` | string | No | `''` | Optional branch push token for `push_to_fork` mode. Falls back to `token`, then `github.token`, but fork mode should use an explicit token with write access to the fork. |
 
 Sensitive values should be passed through action inputs using workflow secrets when you do not want to rely on `github.token`, for example `token: ${{ secrets.SPLICE_BOT_TOKEN }}`.
+Test-only internal inputs such as `bridge_override_json` are intentionally undocumented outside the local test harness context and may change without notice.
 
 ## Sensitive `splice-wf-run` action inputs
 
diff --git a/tests/actions/assert/log_contains.sh b/tests/actions/assert/log_contains.sh
new file mode 100755
index 0000000..ece05a0
--- /dev/null
+++ b/tests/actions/assert/log_contains.sh
@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+log_file="$1"
+expected_marker="$2"
+
+if ! grep -F -- "$expected_marker" "$log_file" >/dev/null 2>&1; then
+  echo "Expected log marker not found: $expected_marker" >&2
+  echo "--- begin log ---" >&2
+  cat "$log_file" >&2
+  echo "--- end log ---" >&2
+  exit 1
+fi
+
diff --git a/tests/actions/events/pr-review-comment-basic.expected b/tests/actions/events/pr-review-comment-basic.expected
new file mode 100644
index 0000000..f389bbb
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-basic.expected
@@ -0,0 +1 @@
+Trigger keyword: (none)
diff --git a/tests/actions/events/pr-review-comment-basic.json b/tests/actions/events/pr-review-comment-basic.json
new file mode 100644
index 0000000..9cf3f27
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-basic.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Please split this out.\n\nsplice-bot",
+    "id": 102,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 43,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "3333333333333333333333333333333333333333",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "4444444444444444444444444444444444444444",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-carriage-return.expected b/tests/actions/events/pr-review-comment-carriage-return.expected
new file mode 100644
index 0000000..f389bbb
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-carriage-return.expected
@@ -0,0 +1 @@
+Trigger keyword: (none)
diff --git a/tests/actions/events/pr-review-comment-carriage-return.json b/tests/actions/events/pr-review-comment-carriage-return.json
new file mode 100644
index 0000000..f8b3849
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-carriage-return.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Please split this.\r\n\r\nsplice-bot\r\n",
+    "id": 109,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 50,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "ffffffffffffffffffffffffffffffffffffffff",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "1212121212121212121212121212121212121212",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-empty-keyword-line.expected b/tests/actions/events/pr-review-comment-empty-keyword-line.expected
new file mode 100644
index 0000000..f389bbb
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-empty-keyword-line.expected
@@ -0,0 +1 @@
+Trigger keyword: (none)
diff --git a/tests/actions/events/pr-review-comment-empty-keyword-line.json b/tests/actions/events/pr-review-comment-empty-keyword-line.json
new file mode 100644
index 0000000..6d160a1
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-empty-keyword-line.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "splice-bot    \n\nmore discussion follows",
+    "id": 110,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 51,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "1313131313131313131313131313131313131313",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "1414141414141414141414141414141414141414",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-indented-trigger.expected b/tests/actions/events/pr-review-comment-indented-trigger.expected
new file mode 100644
index 0000000..af5d331
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-indented-trigger.expected
@@ -0,0 +1 @@
+No `splice-bot` found at the start of a line, skipping.
diff --git a/tests/actions/events/pr-review-comment-indented-trigger.json b/tests/actions/events/pr-review-comment-indented-trigger.json
new file mode 100644
index 0000000..d2be6de
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-indented-trigger.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Looks good.\n\n  splice-bot",
+    "id": 104,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 45,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "7777777777777777777777777777777777777777",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "8888888888888888888888888888888888888888",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-keyword-extra-text.expected b/tests/actions/events/pr-review-comment-keyword-extra-text.expected
new file mode 100644
index 0000000..d5db01e
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-keyword-extra-text.expected
@@ -0,0 +1 @@
+Trigger keyword: ready
diff --git a/tests/actions/events/pr-review-comment-keyword-extra-text.json b/tests/actions/events/pr-review-comment-keyword-extra-text.json
new file mode 100644
index 0000000..2d632fa
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-keyword-extra-text.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Please mark this ready.\n\nsplice-bot ready now",
+    "id": 106,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 47,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "cccccccccccccccccccccccccccccccccccccccc",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-keyword.expected b/tests/actions/events/pr-review-comment-keyword.expected
new file mode 100644
index 0000000..d5db01e
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-keyword.expected
@@ -0,0 +1 @@
+Trigger keyword: ready
diff --git a/tests/actions/events/pr-review-comment-keyword.json b/tests/actions/events/pr-review-comment-keyword.json
new file mode 100644
index 0000000..97a80ae
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-keyword.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Please mark this ready.\n\nsplice-bot ready",
+    "id": 103,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 44,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "5555555555555555555555555555555555555555",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "6666666666666666666666666666666666666666",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-missing-pr-fields.expected b/tests/actions/events/pr-review-comment-missing-pr-fields.expected
new file mode 100644
index 0000000..34163fe
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-missing-pr-fields.expected
@@ -0,0 +1 @@
+Missing required PR details (base/head sha/repo).
diff --git a/tests/actions/events/pr-review-comment-missing-pr-fields.json b/tests/actions/events/pr-review-comment-missing-pr-fields.json
new file mode 100644
index 0000000..f91f265
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-missing-pr-fields.json
@@ -0,0 +1,29 @@
+{
+  "comment": {
+    "body": "splice-bot",
+    "id": 108,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 49,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-no-path.expected b/tests/actions/events/pr-review-comment-no-path.expected
new file mode 100644
index 0000000..e0e5888
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-no-path.expected
@@ -0,0 +1 @@
+This review comment is not on a file diff (no .path). Nothing to do.
diff --git a/tests/actions/events/pr-review-comment-no-path.json b/tests/actions/events/pr-review-comment-no-path.json
new file mode 100644
index 0000000..e2c0351
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-no-path.json
@@ -0,0 +1,30 @@
+{
+  "comment": {
+    "body": "splice-bot",
+    "id": 105,
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 46,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "9999999999999999999999999999999999999999",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-no-trigger.expected b/tests/actions/events/pr-review-comment-no-trigger.expected
new file mode 100644
index 0000000..af5d331
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-no-trigger.expected
@@ -0,0 +1 @@
+No `splice-bot` found at the start of a line, skipping.
diff --git a/tests/actions/events/pr-review-comment-no-trigger.json b/tests/actions/events/pr-review-comment-no-trigger.json
new file mode 100644
index 0000000..efd0b0e
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-no-trigger.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Looks good to me.",
+    "id": 101,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 42,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "1111111111111111111111111111111111111111",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "2222222222222222222222222222222222222222",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/events/pr-review-comment-trigger-mid-line.expected b/tests/actions/events/pr-review-comment-trigger-mid-line.expected
new file mode 100644
index 0000000..af5d331
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-trigger-mid-line.expected
@@ -0,0 +1 @@
+No `splice-bot` found at the start of a line, skipping.
diff --git a/tests/actions/events/pr-review-comment-trigger-mid-line.json b/tests/actions/events/pr-review-comment-trigger-mid-line.json
new file mode 100644
index 0000000..93e7d07
--- /dev/null
+++ b/tests/actions/events/pr-review-comment-trigger-mid-line.json
@@ -0,0 +1,31 @@
+{
+  "comment": {
+    "body": "Please run splice-bot here, thanks.",
+    "id": 107,
+    "path": "src/Foo.lean",
+    "user": {
+      "login": "reviewer"
+    }
+  },
+  "pull_request": {
+    "number": 48,
+    "user": {
+      "login": "author",
+      "id": 12345
+    },
+    "base": {
+      "sha": "dddddddddddddddddddddddddddddddddddddddd",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    },
+    "head": {
+      "sha": "eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee",
+      "ref": "feature-branch",
+      "label": "author:feature-branch",
+      "repo": {
+        "full_name": "leanprover-community/SpliceBot"
+      }
+    }
+  }
+}
diff --git a/tests/actions/run_act_smoke.sh b/tests/actions/run_act_smoke.sh
new file mode 100755
index 0000000..b3abb04
--- /dev/null
+++ b/tests/actions/run_act_smoke.sh
@@ -0,0 +1,97 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+root_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+
+cd "$root_dir"
+
+common_args=(
+  --container-architecture linux/amd64
+  --platform ubuntu-latest=catthehacker/ubuntu:act-latest
+  --no-cache-server
+)
+secret_args=()
+
+if [ -n "${GITHUB_TOKEN:-}" ]; then
+  secret_args+=(--secret GITHUB_TOKEN)
+fi
+
+reusable_events=()
+while IFS= read -r event_file; do
+  reusable_events+=("$event_file")
+done < <(find tests/actions/events -maxdepth 1 -type f -name '*.json' | sort)
+
+if [ "${#reusable_events[@]}" -eq 0 ]; then
+  echo "No reusable workflow smoke fixtures found under tests/actions/events" >&2
+  exit 1
+fi
+
+tmp_dir="$(mktemp -d)"
+trap 'rm -rf "$tmp_dir"' EXIT
+docker_config_dir="${tmp_dir}/docker-config"
+mkdir -p "$docker_config_dir"
+printf '{}\n' > "${docker_config_dir}/config.json"
+
+run_act_with_log() {
+  local log_file="$1"
+  shift
+
+  if ! DOCKER_CONFIG="$docker_config_dir" DOCKER_AUTH_CONFIG='{}' "$@" > "$log_file" 2>&1; then
+    echo "act command failed; log follows:" >&2
+    echo "--- begin act log ---" >&2
+    cat "$log_file" >&2
+    echo "--- end act log ---" >&2
+    if grep -F "error getting credentials" "$log_file" >/dev/null 2>&1; then
+      echo "Hint: this looks like a Docker credential-helper problem while pulling the act runner image." >&2
+      echo "Hint: try `docker pull catthehacker/ubuntu:act-latest` manually, or run with a clean Docker config." >&2
+    fi
+    return 1
+  fi
+}
+
+for event_file in "${reusable_events[@]}"; do
+  expected_file="${event_file%.json}.expected"
+  if [ ! -f "$expected_file" ]; then
+    echo "Missing expected marker file for ${event_file}: ${expected_file}" >&2
+    exit 1
+  fi
+
+  log_file="${tmp_dir}/$(basename "${event_file%.json}").log"
+  echo "==> Running reusable workflow smoke case: ${event_file}"
+  act_args=(
+    act
+    --workflows tests/actions/workflows/splice_harness.yaml
+    --eventpath "$event_file"
+    "${common_args[@]}"
+  )
+  if [ -n "${GITHUB_TOKEN:-}" ]; then
+    act_args+=(--secret GITHUB_TOKEN)
+  fi
+  act_args+=(pull_request_review_comment)
+  run_act_with_log "$log_file" "${act_args[@]}"
+
+  while IFS= read -r expected_marker || [ -n "$expected_marker" ]; do
+    [ -z "$expected_marker" ] && continue
+    if ! tests/actions/assert/log_contains.sh "$log_file" "$expected_marker"; then
+      echo "Reusable smoke case log:" >&2
+      echo "--- begin act log ---" >&2
+      cat "$log_file" >&2
+      echo "--- end act log ---" >&2
+      exit 1
+    fi
+  done < "$expected_file"
+done
+
+echo "==> Running composite action smoke harness"
+composite_log_file="${tmp_dir}/splice_action_harness.log"
+act_args=(
+  act
+  --workflows tests/actions/workflows/splice_action_harness.yaml
+  "${common_args[@]}"
+)
+if [ -n "${GITHUB_TOKEN:-}" ]; then
+  act_args+=(--secret GITHUB_TOKEN)
+fi
+act_args+=(workflow_dispatch)
+run_act_with_log "$composite_log_file" "${act_args[@]}"
diff --git a/tests/actions/workflows/splice_action_harness.yaml b/tests/actions/workflows/splice_action_harness.yaml
new file mode 100644
index 0000000..f8f7cc3
--- /dev/null
+++ b/tests/actions/workflows/splice_action_harness.yaml
@@ -0,0 +1,136 @@
+name: Splice Action Act Harness
+
+on:
+  workflow_dispatch:
+
+permissions: {}
+
+jobs:
+  invalid-bridge-override-json:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run invalid bridge override case
+        id: invalid_bridge_override
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          bridge_override_json: >-
+            ["not","an","object"]
+
+      - name: Assert invalid bridge override failed
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.invalid_bridge_override.outcome }}" = "failure" ]
+
+  invalid-min-repo-permission:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run invalid permission case
+        id: invalid_permission
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          min_repo_permission: bogus
+          bridge_override_json: >-
+            {"file_path":"src/Foo.lean","commenter_login":"reviewer","pr_author_login":"author","base_ref":"master","base_repo":"leanprover-community/SpliceBot","head_repo":"leanprover-community/SpliceBot","head_sha":"1111111111111111111111111111111111111111","head_ref":"feature","head_label":"author:feature","committer":"github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>","author":"author <12345+author@users.noreply.github.com>"}
+
+      - name: Assert invalid permission failed
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.invalid_permission.outcome }}" = "failure" ]
+
+  invalid-base-repo-format:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run invalid base repo format case
+        id: invalid_base_repo
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          bridge_override_json: >-
+            {"file_path":"src/Foo.lean","commenter_login":"reviewer","pr_author_login":"author","base_ref":"master","base_repo":"not-a-repo","head_repo":"leanprover-community/SpliceBot","head_sha":"1111111111111111111111111111111111111111","head_ref":"feature","head_label":"author:feature","committer":"github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>","author":"author <12345+author@users.noreply.github.com>"}
+
+      - name: Assert invalid base repo format failed
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.invalid_base_repo.outcome }}" = "failure" ]
+
+  missing-bridge-data:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run missing bridge data case
+        id: missing_bridge
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          bridge_override_json: >-
+            {"file_path":"src/Foo.lean","commenter_login":"reviewer","base_ref":"master","base_repo":"leanprover-community/SpliceBot","head_repo":"leanprover-community/SpliceBot","head_sha":"1111111111111111111111111111111111111111","head_ref":"feature","head_label":"author:feature","committer":"github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>","author":"author <12345+author@users.noreply.github.com>"}
+
+      - name: Assert missing bridge data failed
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.missing_bridge.outcome }}" = "failure" ]
+
+  authorized-pr-author-then-checkout-fails:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run pr-author authorization success case
+        id: pr_author_checkout_failure
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          allow_pr_author: 'true'
+          bridge_override_json: >-
+            {"file_path":"src/Foo.lean","commenter_login":"author","pr_author_login":"author","pr_number":"1","review_comment_id":"1","base_ref":"master","base_repo":"example/definitely-does-not-exist","head_repo":"example/definitely-does-not-exist","head_sha":"1111111111111111111111111111111111111111","head_ref":"feature","head_label":"author:feature","committer":"github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>","author":"author <12345+author@users.noreply.github.com>"}
+
+      - name: Assert pr-author auth succeeded before later failure
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.pr_author_checkout_failure.outcome }}" = "failure" ]
+
+  allowed-user-then-checkout-fails:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Run allowed user authorization success case
+        id: allowed_user_checkout_failure
+        continue-on-error: true
+        uses: ./.github/actions/splice-wf-run
+        with:
+          source_workflow: act-harness
+          allowed_users: reviewer
+          bridge_override_json: >-
+            {"file_path":"src/Foo.lean","commenter_login":"reviewer","pr_author_login":"author","pr_number":"1","review_comment_id":"1","base_ref":"master","base_repo":"example/definitely-does-not-exist","head_repo":"example/definitely-does-not-exist","head_sha":"1111111111111111111111111111111111111111","head_ref":"feature","head_label":"author:feature","committer":"github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>","author":"author <12345+author@users.noreply.github.com>"}
+
+      - name: Assert allowed user auth succeeded before later failure
+        shell: bash
+        run: |
+          set -euo pipefail
+          [ "${{ steps.allowed_user_checkout_failure.outcome }}" = "failure" ]
diff --git a/tests/actions/workflows/splice_harness.yaml b/tests/actions/workflows/splice_harness.yaml
new file mode 100644
index 0000000..cc47c3c
--- /dev/null
+++ b/tests/actions/workflows/splice_harness.yaml
@@ -0,0 +1,17 @@
+name: Splice Act Harness
+
+on:
+  pull_request_review_comment:
+    types:
+      - created
+      - edited
+
+permissions: {}
+
+jobs:
+  run-reusable:
+    uses: ./.github/workflows/splice.yaml
+    with:
+      base_ref: master
+      emit_bridge_artifact: false
+