fix(sf): guard auto-loop against missing DB and missing basePath

Two small defensive fixes in the auto-loop that surfaced when running
sf in degraded environments (no .sf/sf.db yet, or unset basePath):

- phases.ts: gate planning-flow gate behind isDbAvailable() so a missing or
  not-yet-initialized DB does not throw inside the gate runner.
- run-unit.ts: skip process.chdir when s.basePath is falsy. The original
  guard compared cwd to an empty string, which always failed on the first
  unit of a fresh runtime root.

Both are conservative — preserve existing behaviour when DB and basePath
are present.

src/resources/extensions/sf/auto/phases.ts

@@ -596,7 +596,7 @@ export async function runPreDispatch(
 
 	// Derive state
 	let state = await deps.deriveState(s.basePath);
-	if (uokFlags.planningFlow && shouldRunPlanningFlowGate(state.phase)) {
+	if (uokFlags.planningFlow && isDbAvailable() && shouldRunPlanningFlowGate(state.phase)) {
 		let compiled = ensurePlanningFlowGraph(s.basePath, state);
 		// Empty-graph recovery: stale DB caches can yield 0 nodes right after a
 		// task-complete write. Invalidate caches, re-derive state, and retry once.

src/resources/extensions/sf/auto/run-unit.ts

@@ -52,7 +52,7 @@ export async function runUnit(
 	// wrong directory. Must be synchronous — no awaits between chdir and
 	// newSession (#1389, #4762 follow-up).
 	try {
-		if (process.cwd() !== s.basePath) {
+		if (s.basePath && process.cwd() !== s.basePath) {
 			process.chdir(s.basePath);
 		}
 	} catch (e) {