Persist sidechain runtime metadata

Author: SqlRush

docs/first-second-parity-audit.md

@@ -238,6 +238,7 @@ M6 progress now includes:
 - `internal/contracts`/`internal/session`: remote-history `SDKEvent.message` now accepts top-level string and content-block array payloads, wrapping them as message content before event decoding so provider-shaped assistant/user events still materialize into transcript messages (`TestSDKEventUnmarshalAcceptsScalarMessagePayload`, `TestRemoteHistoryTranscriptMessagesAcceptsScalarEventMessagePayload`).
 - `internal/contracts`/`internal/session`: remote-history `SDKEvent` status/error/result payloads now accept adjacent field aliases such as `statusMessage`, `progress_message`, `errorMessage`, `failure_reason`, `resultText`, `outputText`, and result object aliases including `output`, `response`, `value`, and `completion`, scoped to the matching canonical event type (`TestSDKEventUnmarshalAcceptsStatusErrorResultAliases`, `TestRemoteHistoryEventsAcceptStatusErrorResultAliases`).
 - `internal/contracts`/`internal/session`: remote-history `SDKEvent` type canonicalization now also accepts adjacent stream/provider aliases such as `assistant_delta`, `humanMessage`, `finalResult`, `response.completed`, `failureEvent`, and `statusMessage`, keeping transcript materialization stable across SDK event spellings.
+- `internal/session`: sidechain runtime start now persists agent type, worktree path, and task description into the lifecycle transcript payload as well as the metadata sidecar, so resume/list can recover subagent metadata even if the sidecar is missing.
 - `internal/memory`: memory age/freshness helpers now match official stale-memory guidance, and document loading can prefix old memory files with a system-reminder that they are point-in-time observations.
 - `internal/memory`: relevant-memory attachment primitives now match the official `relevant_memories` shape for stable headers, system-reminder rendering, surfaced path/byte scanning, 200-line/4096-byte surfacing reads with truncation notices, mark-after-filter duplicate attachment handling, last-non-meta-user/single-word/session-byte-cap prefetch gating, top-5 candidate filtering after read-state/surfaced de-dup, and recent successful tools collection excluding pending/failed/same-name-failed tools.
 - `internal/conversation`: request building now expands `relevant_memories` attachment messages into user/meta system-reminders before Anthropic API normalization.

internal/session/sidechain_runtime.go

@@ -90,10 +90,12 @@ func (r SidechainRuntime) Start(options SidechainOptions) (SidechainRun, error)
 		Subtype:     "sidechain_start",
 		IsSidechain: true,
 		Content: map[string]any{
-			"sidechainId": id,
-			"agentId":     id,
-			"status":      run.Status,
-			"agentType":   options.AgentType,
+			"sidechainId":  id,
+			"agentId":      id,
+			"status":       run.Status,
+			"agentType":    options.AgentType,
+			"worktreePath": options.WorktreePath,
+			"description":  options.Description,
 		},
 	}); err != nil {
 		return SidechainRun{}, err

internal/session/sidechain_test.go

@@ -115,6 +115,40 @@ func TestSidechainRuntimeStartAppendFinish(t *testing.T) {
 	}
 }
 
+func TestSidechainRuntimeStartPersistsMetadataInLifecyclePayload(t *testing.T) {
+	sessionPath := filepath.Join(t.TempDir(), "session.jsonl")
+	sessionID := contracts.ID("sess_1")
+	runtime := SidechainRuntime{SessionPath: sessionPath, SessionID: sessionID}
+	run, err := runtime.Start(SidechainOptions{
+		ID:           "agent/meta",
+		StartedAt:    time.Unix(100, 0).UTC(),
+		AgentType:    "researcher",
+		WorktreePath: "/tmp/research-worktree",
+		Description:  "research the migration",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Remove(run.MetadataPath); err != nil {
+		t.Fatal(err)
+	}
+
+	state, err := FindSidechainState(sessionPath, sessionID, "agent/meta")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if state.Status != SidechainStatusRunning {
+		t.Fatalf("state = %#v", state)
+	}
+	if state.Metadata.AgentType != "researcher" || state.Metadata.WorktreePath != "/tmp/research-worktree" || state.Metadata.Description != "research the migration" {
+		t.Fatalf("metadata recovered from lifecycle payload = %#v", state.Metadata)
+	}
+	resumed, ok := ResumeSidechainRunFromState(state)
+	if !ok || resumed.Metadata.AgentType != "researcher" || resumed.Metadata.WorktreePath != "/tmp/research-worktree" || resumed.Metadata.Description != "research the migration" {
+		t.Fatalf("resumed = %#v ok=%v", resumed, ok)
+	}
+}
+
 func TestLoadSidechainStateMarksOrphanTranscriptUnknown(t *testing.T) {
 	sessionPath := filepath.Join(t.TempDir(), "session.jsonl")
 	sessionID := contracts.ID("sess_1")