feat(prd-1): implement M1 - platform detection and action.yml modifications

- Add src/platform/detector.ts with 3-tier detection (explicit input,
  FORGEJO env var, GITHUB_SERVER_URL heuristic)
- Add 'platform' input to action.yml (auto/github/forgejo)
- Add 'Detect Platform' shell step as first composite action step
- Split bun installation: oven-sh/setup-bun for GitHub, curl fallback
  for Forgejo runners
- Condition 'Revoke app token' step to skip on Forgejo
- Pass resolved PLATFORM env var to run step
- Add 14 unit tests covering all detection paths

Progress: M1 complete (1/9 milestones) - M2 and M5 now unblocked

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

action.yml

@@ -138,6 +138,12 @@ inputs:
     required: false
     default: ""
 
+  # Platform configuration
+  platform:
+    description: "Platform to run on: 'auto' (default auto-detects), 'github', or 'forgejo'"
+    required: false
+    default: "auto"
+
 outputs:
   execution_file:
     description: "Path to the Claude Code execution output file"
@@ -158,13 +164,43 @@ outputs:
 runs:
   using: "composite"
   steps:
+    - name: Detect Platform
+      id: detect-platform
+      shell: bash
+      run: |
+        if [ "${{ inputs.platform }}" = "forgejo" ]; then
+          DETECTED="forgejo"
+        elif [ "${{ inputs.platform }}" = "github" ]; then
+          DETECTED="github"
+        elif [ "${FORGEJO}" = "true" ]; then
+          DETECTED="forgejo"
+        elif [ -n "${GITHUB_SERVER_URL}" ] && echo "${GITHUB_SERVER_URL}" | grep -qv "github.com"; then
+          DETECTED="forgejo"
+        else
+          DETECTED="github"
+        fi
+        echo "platform=${DETECTED}" >> "$GITHUB_OUTPUT"
+        echo "Detected platform: ${DETECTED}"
+
     - name: Install Bun
-      if: inputs.path_to_bun_executable == ''
+      if: inputs.path_to_bun_executable == '' && steps.detect-platform.outputs.platform != 'forgejo'
       uses: oven-sh/setup-bun@3d267786b128fe76c2f16a390aa2448b815359f3 # https://github.com/oven-sh/setup-bun/releases/tag/v2.1.2
       with:
         bun-version: 1.3.6
         token: ${{ inputs.github_token || github.token }}
 
+    - name: Install Bun (Forgejo)
+      if: inputs.path_to_bun_executable == '' && steps.detect-platform.outputs.platform == 'forgejo'
+      shell: bash
+      run: |
+        if command -v bun &> /dev/null; then
+          echo "Bun is already installed: $(bun --version)"
+        else
+          echo "Installing Bun via curl..."
+          curl -fsSL https://bun.sh/install | bash
+          echo "$HOME/.bun/bin" >> "$GITHUB_PATH"
+        fi
+
     - name: Setup Custom Bun Path
       if: inputs.path_to_bun_executable != ''
       shell: bash
@@ -188,6 +224,9 @@ runs:
       run: |
         bun run ${GITHUB_ACTION_PATH}/src/entrypoints/run.ts
       env:
+        # Platform detection
+        PLATFORM: ${{ steps.detect-platform.outputs.platform }}
+
         # Prepare inputs
         MODE: ${{ inputs.mode }}
         PROMPT: ${{ inputs.prompt }}
@@ -283,7 +322,7 @@ runs:
         bun run ${GITHUB_ACTION_PATH}/src/entrypoints/cleanup-ssh-signing.ts
 
     - name: Revoke app token
-      if: always() && inputs.github_token == '' && steps.run.outputs.skipped_due_to_workflow_validation_mismatch != 'true'
+      if: always() && inputs.github_token == '' && steps.run.outputs.skipped_due_to_workflow_validation_mismatch != 'true' && steps.detect-platform.outputs.platform != 'forgejo'
       shell: bash
       run: |
         curl -L \

prds/1-forgejo-platform-support.md

@@ -228,7 +228,7 @@ The upstream repo has 13 workflows in `.github/workflows/`. Strategy:
 
 ### Phase 1 - Foundation (parallel, no dependencies)
 
-- [ ] **M1: Platform detection + `action.yml` modifications** — Add `platform` input to `action.yml`. Create `src/platform/detector.ts` with explicit input + env-var auto-detection. Add conditional logic to skip "Revoke app token" step on Forgejo. Fix bun installation to handle Forgejo runners (direct curl fallback).
+- [x] **M1: Platform detection + `action.yml` modifications** — Add `platform` input to `action.yml`. Create `src/platform/detector.ts` with explicit input + env-var auto-detection. Add conditional logic to skip "Revoke app token" step on Forgejo. Fix bun installation to handle Forgejo runners (direct curl fallback).
   - Files: `action.yml` (MODIFIED), `src/platform/detector.ts` (NEW)
   - Success: `detectPlatform()` returns "forgejo" in Forgejo runner, "github" in GitHub runner. `action.yml` doesn't error on Forgejo.
 

src/platform/detector.ts

@@ -0,0 +1,29 @@
+/**
+ * Platform detection for GitHub vs Forgejo environments.
+ *
+ * Detection priority:
+ * 1. PLATFORM env var (set by action.yml detect step or explicit input)
+ * 2. FORGEJO env var (set by Forgejo runner v7.0+)
+ * 3. GITHUB_SERVER_URL heuristic (non-github.com = Forgejo)
+ * 4. Default to GitHub
+ */
+
+export type Platform = "github" | "forgejo";
+
+export function detectPlatform(): Platform {
+  // 1. Explicit platform from action.yml detect step or user input
+  const platformEnv = process.env.PLATFORM;
+  if (platformEnv === "forgejo") return "forgejo";
+  if (platformEnv === "github") return "github";
+
+  // 2. FORGEJO env var (set by Forgejo runner v7.0+)
+  if (process.env.FORGEJO === "true") return "forgejo";
+
+  // 3. GITHUB_SERVER_URL heuristic — if not github.com, likely Forgejo/Gitea
+  const serverUrl = process.env.GITHUB_SERVER_URL || "";
+  if (serverUrl && !serverUrl.includes("github.com")) {
+    return "forgejo";
+  }
+
+  return "github";
+}

test/platform-detector.test.ts

@@ -0,0 +1,94 @@
+import { detectPlatform } from "../src/platform/detector";
+import { describe, it, expect, beforeEach } from "bun:test";
+
+describe("detectPlatform", () => {
+  beforeEach(() => {
+    // Reset relevant env vars before each test
+    delete process.env.PLATFORM;
+    delete process.env.FORGEJO;
+    delete process.env.GITHUB_SERVER_URL;
+  });
+
+  // Restore original env after all tests in this file
+  // (bun:test doesn't have afterAll cleanup issues like jest, but let's be safe)
+
+  describe("explicit PLATFORM env var", () => {
+    it("should return 'forgejo' when PLATFORM is 'forgejo'", () => {
+      process.env.PLATFORM = "forgejo";
+      expect(detectPlatform()).toBe("forgejo");
+    });
+
+    it("should return 'github' when PLATFORM is 'github'", () => {
+      process.env.PLATFORM = "github";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should take precedence over FORGEJO env var", () => {
+      process.env.PLATFORM = "github";
+      process.env.FORGEJO = "true";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should take precedence over GITHUB_SERVER_URL", () => {
+      process.env.PLATFORM = "github";
+      process.env.GITHUB_SERVER_URL = "https://git.example.com";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should ignore unrecognized PLATFORM values and fall through", () => {
+      process.env.PLATFORM = "gitlab";
+      // No other env vars set, should default to github
+      expect(detectPlatform()).toBe("github");
+    });
+  });
+
+  describe("FORGEJO env var", () => {
+    it("should return 'forgejo' when FORGEJO is 'true'", () => {
+      process.env.FORGEJO = "true";
+      expect(detectPlatform()).toBe("forgejo");
+    });
+
+    it("should not detect forgejo when FORGEJO is 'false'", () => {
+      process.env.FORGEJO = "false";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should not detect forgejo when FORGEJO is empty", () => {
+      process.env.FORGEJO = "";
+      expect(detectPlatform()).toBe("github");
+    });
+  });
+
+  describe("GITHUB_SERVER_URL heuristic", () => {
+    it("should return 'forgejo' for non-github.com server URLs", () => {
+      process.env.GITHUB_SERVER_URL = "https://git.wxs.ro";
+      expect(detectPlatform()).toBe("forgejo");
+    });
+
+    it("should return 'forgejo' for gitea/forgejo instances", () => {
+      process.env.GITHUB_SERVER_URL = "https://forgejo.example.org";
+      expect(detectPlatform()).toBe("forgejo");
+    });
+
+    it("should return 'github' for github.com", () => {
+      process.env.GITHUB_SERVER_URL = "https://github.com";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should return 'github' for GitHub Enterprise (contains github.com)", () => {
+      process.env.GITHUB_SERVER_URL = "https://github.com/enterprise";
+      expect(detectPlatform()).toBe("github");
+    });
+
+    it("should return 'github' when GITHUB_SERVER_URL is empty", () => {
+      process.env.GITHUB_SERVER_URL = "";
+      expect(detectPlatform()).toBe("github");
+    });
+  });
+
+  describe("default behavior", () => {
+    it("should return 'github' when no env vars are set", () => {
+      expect(detectPlatform()).toBe("github");
+    });
+  });
+});