SIENTIAPDE-2226: Stop installing runtime in worker; unpin requirements

- The sientia-module entrypoint now merges requirements.txt with the
  Plugin Store runtime and installs both before boot (SIENTIAPDE-2223),
  so the worker no longer calls install_runtime or runs the loaded
  package version guard.
- Leave runtime libs unpinned in requirements files so the runtime
  version wins; cap sqlalchemy<2.1 and evidently<0.7 for compatibility.
- Update README, CLAUDE.md and worker tests to match.

model_manager/worker/worker.py

@@ -32,7 +32,6 @@ from temporalio.runtime import PrometheusConfig, Runtime, TelemetryConfig
 
 with workflow.unsafe.imports_passed_through():
     import asyncio
-    import importlib.metadata
     import os
     import sys
 
@@ -77,36 +76,6 @@ def _get_runtime(runtime: str | None) -> str:
     return normalized_runtime or 'single'
 
 
-def _loaded_distribution_versions() -> dict[str, str]:
-    """Version on disk of every installed distribution whose top-level module is imported."""
-    # Iterate a copy: another thread importing while we iterate would raise RuntimeError.
-    loaded = {name.partition('.')[0] for name in sys.modules.copy()}
-    return {
-        dist: importlib.metadata.version(dist)
-        for module, dists in importlib.metadata.packages_distributions().items()
-        if module in loaded
-        for dist in dists
-    }
-
-
-def _runtime_changed_loaded_packages(before: dict[str, str]) -> dict[str, str]:
-    """
-    Packages that were imported before ``install_runtime`` and whose version changed on disk.
-
-    The process keeps the old code in memory, so a later lazy import mixes two versions
-    (SIENTIAPDE-2214: sklearn 1.9.1 in memory, 1.8.0 on disk, ``_cyutility`` import error).
-    """
-    changed = {}
-    for dist, old in before.items():
-        try:
-            new = importlib.metadata.version(dist)
-        except importlib.metadata.PackageNotFoundError:
-            new = 'removed'
-        if new != old:
-            changed[dist] = f'{old} -> {new}'
-    return changed
-
-
 async def main():
     """
     Main entry point for the Model Manager worker application.
@@ -114,9 +83,9 @@ async def main():
     This function initializes and starts all components of the worker:
     1. Sets up logging and metadata
     2. Starts Prometheus metrics server
-    3. Initializes notification handler, then installs the runtime; exits if the install
-       changed the version of a package the worker already imported, and only then sets
-       ``app_up`` (what the probes check) to 1
+    3. Initializes notification handler and Plugin Store client, then sets ``app_up``
+       (what the probes check) to 1. The runtime libraries are already installed: the
+       sientia-module entrypoint merges them into the resolved requirements before boot
     4. Creates and configures activities
     5. Starts Temporal client and workers
     6. Manages worker lifecycle and graceful shutdown
@@ -158,8 +127,6 @@ async def main():
 
     metrics_controller = MetricsController(logger=logger)
 
-    logger.custom_info(f'Installing runtime {runtime}', metadata)
-
     plugin_store_parameters = build_plugin_store_config()
     plugin_store = PluginStore(
         base_url=plugin_store_parameters['base_url'],
@@ -177,21 +144,7 @@ async def main():
         metrics_controller=metrics_controller,
     )
 
-    loaded_before_install = _loaded_distribution_versions()
-    await plugin_store.install_runtime(runtime_name=runtime)
-
-    changed = _runtime_changed_loaded_packages(loaded_before_install)
-    if changed:
-        logger.custom_critical(
-            f'Runtime {runtime} changed packages already imported by the worker: {changed}. '
-            'Pin them in requirements.txt to the runtime versions.',
-            metadata,
-        )
-        metrics.APP_UP.labels(pod_id=POD_ID).set(0)
-        sys.exit(1)
-
-    # The probes only check app_up, so it goes to 1 after the guard: a pod that would fail it
-    # never turns Ready, and a rollout keeps the old pod.
+    # The probes only check app_up, so it goes to 1 only after initialization.
     metrics.APP_UP.labels(pod_id=POD_ID).set(1)
 
     activities = Activities(
@@ -281,7 +234,7 @@ def start_prometheus_server(logger: SientiaLogger, metadata: dict[str, str | Non
     Starts the Prometheus metrics server for monitoring and observability.
 
     This function initializes the Prometheus HTTP server on the configured port.
-    ``main`` sets ``app_up`` to 1 later, once the runtime install passed the version guard.
+    ``main`` sets ``app_up`` to 1 later, once initialization is done.
 
     The server exposes metrics that can be scraped by Prometheus for monitoring
     the health and performance of the Model Manager worker.