fix(inference): tolerate a briefly-absent provider instead of killing the session (#299)

A transient provider connection drop (e.g. OOM-killed llama.cpp mid-request)
collapsed into a hard NoEligibleProviderException that escaped runInference's
try/catch (the route() call sat outside it), propagated past the stage retry
loop, and landed in ServerModule's session-level catch — failing the WHOLE
session even though the failure was retryable and the provider recovered
seconds later.

- SessionOrchestrator.runInference: wrap router.route() in try/catch so
  routing failures become InferenceResult.Failed and flow through the normal
  retryable/backoff/exhaustion machinery instead of escaping.
- DefaultInferenceRouter.route: distinguish "capability never configured on
  any provider" (fail fast, waiting can't help) from "configured but
  currently unhealthy" (bounded wait/backoff — default 3 attempts x 2s —
  re-checking health before declaring NoEligibleProvider terminal).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GeyGFXczJb8RUWGBKmkm6G

core/kernel/src/main/kotlin/com/correx/core/kernel/orchestration/SessionOrchestrator.kt

@@ -300,7 +300,15 @@ abstract class SessionOrchestrator(
         // ToolCalling score and routes the stage to the best tool-caller.
         val requiredCapabilities = stageConfig.requiredCapabilities +
             if (withTools && stageConfig.allowedTools.isNotEmpty()) setOf(ModelCapability.ToolCalling) else emptySet()
-        val provider = inferenceRouter.route(stageId, requiredCapabilities, stageConfig.modelId)
+        // Routing itself can fail transiently (provider mid-crash-recovery) — it must be retryable
+        // like any other inference failure, not escape and kill the whole session (see #299).
+        val provider = try {
+            inferenceRouter.route(stageId, requiredCapabilities, stageConfig.modelId)
+        } catch (e: CancellationException) {
+            throw e
+        } catch (e: Exception) {
+            return InferenceResult.Failed(e.message ?: "routing failed")
+        }
         log.debug(
             "[Orchestrator] inference session={} stage={} provider={} timeoutMs={}",
             sessionId.value, stageId.value, provider.id.value, timeoutMs,