fix(context): emit the manifest on every context rebuild, not just the first (#307)

c742656e emitted ContextAssembledEvent only at the stage's initial
contextPackBuilder.build. But the question that motivated #307 — "did the ACR
steer-away hint fire on 7 consecutive turns?" — is a per-rebuild question:
unconfirmedFixEntries recomputes on every rebuild, which is exactly the #306
bug. With one event per stage the log still couldn't answer it.

Emit at all four build sites, matching emitContextTruncationIfNeeded's existing
placement: pushBack, the tool-round rebuild, and the tools-less clean emission.

./gradlew check green.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HgDL1v3GuQ9RZnYR6fDT95

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

@@ -367,6 +367,7 @@ internal suspend fun SessionOrchestrator.executeStage(
             budget = TokenBudget(limit = stageConfig.tokenBudget),
         )
         emitContextTruncationIfNeeded(sessionId, stageId, currentContext)
+        emitContextAssembled(sessionId, stageId, currentContext)
         toolRounds++
         return runInference(
             sessionId, stageId, currentContext, stageConfig, config.stageTimeoutMs, responseFormat, effectives,
@@ -546,6 +547,7 @@ internal suspend fun SessionOrchestrator.executeStage(
             budget = TokenBudget(limit = stageConfig.tokenBudget),
         )
         emitContextTruncationIfNeeded(sessionId, stageId, currentContext)
+        emitContextAssembled(sessionId, stageId, currentContext)
         inferenceResult = runInference(
             sessionId, stageId, currentContext, stageConfig, config.stageTimeoutMs, responseFormat, effectives,
         )
@@ -579,6 +581,7 @@ internal suspend fun SessionOrchestrator.executeStage(
                 entries = accumulatedEntries,
                 budget = TokenBudget(limit = stageConfig.tokenBudget),
             )
+            emitContextAssembled(sessionId, stageId, currentContext)
             inferenceResult = runInference(
                 sessionId, stageId, currentContext, stageConfig, config.stageTimeoutMs,
                 responseFormat, effectives, withTools = false,