ci: add release-please for versioned, self-describing contract releases

scale-agentex has no version axis of its own — it floats at head, and the only
version concept comes from SGP's platform release. That leaves no way to name an
"oldest supported server contract" for downstream consumers.

Add release-please (release-type: python; conventional-commit PR titles already
enforced) so merges to main cut versioned releases: a vX.Y.Z git tag + GitHub
release + CHANGELOG.

Make the contract self-describe its version so the tag and spec never drift:
- src/_version.py is the single source; the FastAPI app reads it
  (version=__version__), so generate_openapi_spec.py emits it as info.version.
- release-please bumps src/_version.py, agentex/openapi.yaml (info.version),
  agentex/pyproject.toml, and the root pyproject together with the tag.

Each tag is thus an immutable, self-describing snapshot of agentex/openapi.yaml
the SDK's cross-version compat suite can pin as min-supported
(scaleapi/scale-agentex-python#407), replacing the placeholder commit SHA today.

Contract checkpoints, not a deploy gate: the server still floats at head for
deploys. Seeded at 0.1.0 with bootstrap-sha at current main HEAD so the
changelog starts fresh; the first feat/fix merge (or workflow_dispatch) cuts the
first release. Verified gen-openapi emits info.version from _version.py with no
spec drift.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: max-parke-scale

.github/workflows/release-please.yml

@@ -0,0 +1,24 @@
+name: release-please
+
+# Cuts versioned contract-checkpoint releases (tag + GitHub release + CHANGELOG)
+# from conventional commits. These are contract snapshots, NOT a deploy gate.
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    if: github.repository == 'scaleapi/scale-agentex'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: googleapis/release-please-action@5c625bfb5d1ff62eadeeb3772007f7f66fdcf071 # v4.4.1
+        with:
+          config-file: release-please-config.json
+          manifest-file: .release-please-manifest.json

.release-please-manifest.json

@@ -0,0 +1,3 @@
+{
+  ".": "0.1.0"
+}

agentex/src/_version.py

@@ -0,0 +1,3 @@
+"""Single source of the agentex contract version (bumped by release-please)."""
+
+__version__ = "0.1.0"  # x-release-please-version

agentex/src/api/app.py

@@ -21,6 +21,7 @@
 from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
 
+from src._version import __version__
 from src.adapters.crud_store.exceptions import ItemDoesNotExist
 from src.adapters.http.adapter_httpx import HttpxGateway
 from src.api.authentication_middleware import AgentexAuthMiddleware
@@ -108,6 +109,7 @@ async def lifespan(_: FastAPI):
 
 fastapi_app = FastAPI(
     title="Agentex API",
+    version=__version__,
     openapi_url="/openapi.json",
     docs_url="/swagger",
     redoc_url="/api",

release-please-config.json

@@ -0,0 +1,32 @@
+{
+  "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
+  "include-v-in-tag": true,
+  "include-component-in-tag": false,
+  "bump-minor-pre-major": true,
+  "bump-patch-for-minor-pre-major": false,
+  "bootstrap-sha": "ab469df91bba043ea25356c89147d29f7df03bad",
+  "changelog-sections": [
+    { "type": "feat", "section": "Features" },
+    { "type": "fix", "section": "Bug Fixes" },
+    { "type": "perf", "section": "Performance Improvements" },
+    { "type": "revert", "section": "Reverts" },
+    { "type": "docs", "section": "Documentation" },
+    { "type": "refactor", "section": "Refactors" },
+    { "type": "chore", "section": "Chores", "hidden": true },
+    { "type": "test", "section": "Tests", "hidden": true },
+    { "type": "ci", "section": "Continuous Integration", "hidden": true },
+    { "type": "build", "section": "Build System", "hidden": true },
+    { "type": "style", "section": "Styles", "hidden": true }
+  ],
+  "packages": {
+    ".": {
+      "release-type": "python",
+      "package-name": "agentex",
+      "extra-files": [
+        "agentex/src/_version.py",
+        { "type": "yaml", "path": "agentex/openapi.yaml", "jsonpath": "$.info.version" },
+        { "type": "toml", "path": "agentex/pyproject.toml", "jsonpath": "$.project.version" }
+      ]
+    }
+  }
+}