feat: caller dictates the cache log path; drop RUN_DIR

.env.example

@@ -39,7 +39,5 @@ OIDC_AUDIENCES=
 # --- Cache process management ----------------------------------------------
 # Path to the fastcache executable; bare name = resolved via PATH.
 FASTCACHE_BINARY=lclstream-fastcache
-# Directory where per-cache config/log files are written.
-RUN_DIR=run
 # Grace period (seconds) before escalating SIGTERM to SIGKILL on shutdown.
 SHUTDOWN_GRACE_SECONDS=5.0

src/fastcache_api/config.py

@@ -51,8 +51,6 @@ class Settings(BaseSettings):
     # Cache process management
     # Path to the fastcache executable (overridable; defaults to PATH lookup).
     FASTCACHE_BINARY: Path = Path("lclstream-fastcache")
-    # Directory where per-cache config/log files are written.
-    RUN_DIR: Path = Path("run")
     # Grace period before escalating SIGTERM to SIGKILL on shutdown.
     SHUTDOWN_GRACE_SECONDS: float = 5.0
     # How often the liveness poller checks running caches against their pids.

src/fastcache_api/models.py

@@ -54,6 +54,8 @@ class CacheRequest(BaseModel):
     # Human who initiated the transfer upstream (bearer token is a shared
     # service identity, so attribution must travel in the request body).
     requested_by: str
+    # Absolute path the orchestrator dictates for this cache's log.
+    log_path: Path
 
 
 class CachePublic(BaseModel):

src/fastcache_api/process.py

@@ -3,6 +3,7 @@
 import socket
 import subprocess
 from collections.abc import Iterable
+from pathlib import Path
 from uuid import UUID
 
 import psutil
@@ -35,17 +36,18 @@ def allocate_port_pair(in_use: set[int], start: int, end: int) -> tuple[int, int
     raise RuntimeError(f"no free cache port pair in range [{start}, {end}]")
 
 
-def start_cache(cache_id: UUID, config: CacheConfig) -> CacheProcess:
-    run_dir = settings.RUN_DIR / str(cache_id)
+def start_cache(cache_id: UUID, config: CacheConfig, log_path: Path) -> CacheProcess:
+    run_dir = log_path.parent
     run_dir.mkdir(parents=True, exist_ok=True)
 
     config_path = run_dir / "config.json"
     config_path.write_text(config.to_fastcache_json())
 
-    log_path = (run_dir / "cache.log").resolve()
+    log_path = log_path.resolve()
     with log_path.open("ab") as log_file:
         proc = subprocess.Popen(
             [settings.FASTCACHE_BINARY, config_path],
+            cwd=run_dir,
             stdout=log_file,
             stderr=subprocess.STDOUT,
             start_new_session=True,

src/fastcache_api/routes/cache.py

@@ -91,7 +91,7 @@ async def create_cache(
 
     cache_id = uuid4()
     try:
-        proc = start_cache(cache_id, config)
+        proc = start_cache(cache_id, config, req.log_path)
     except (FileNotFoundError, OSError, RuntimeError) as exc:
         raise HTTPException(
             status_code=status.HTTP_503_SERVICE_UNAVAILABLE,