diff --git a/internal/cli/cache_contract_test.go b/internal/cli/cache_contract_test.go
index c6b0d8e..7595311 100644
--- a/internal/cli/cache_contract_test.go
+++ b/internal/cli/cache_contract_test.go
@@ -249,10 +249,24 @@ func TestRunAutoReusesPlanWhenRunInputsChange(t *testing.T) {
 	}
 	harness.mu.Lock()
 	chunkCalls := harness.chunkCalls
+	sessions := append([]string(nil), harness.sessionIDs...)
 	harness.mu.Unlock()
 	if chunkCalls != 1 {
 		t.Fatalf("chunk calls across changed run inputs = %d, want 1", chunkCalls)
 	}
+	rawInput, err := os.ReadFile(roots.input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantSessionID, err := resolvePromptSessionID("", "test/input", rawInput)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, sessionID := range sessions {
+		if sessionID != wantSessionID {
+			t.Fatalf("session IDs across reference changes = %#v, want %q", sessions, wantSessionID)
+		}
+	}
 	assertFile(t, filepath.Join(roots.plans, strings.TrimPrefix(stateTestDigest, "sha256:"), "plan.json"))
 	assertAnyFile(t, roots.output)
 }
diff --git a/internal/cli/run.go b/internal/cli/run.go
index 578b4e2..9888e4e 100644
--- a/internal/cli/run.go
+++ b/internal/cli/run.go
@@ -418,6 +418,10 @@ func runPipelineCommand(args []string, stdout, stderr io.Writer, opts Options) i
 	if err != nil {
 		return failPipelineCommand(stderr, commandState, terminalWriter, err)
 	}
+	invocation.SessionID = effectiveSessionID
+	if err := writeSummary(summary, func() error { return summary.WriteInvocation(invocation) }); err != nil {
+		return failPipelineCommand(stderr, commandState, terminalWriter, fmt.Errorf("write debug invocation metadata: %w", err))
+	}
 	chunkPlans, err := chunkPlanStoreForRun(effective.Config.Cache.ChunkPlans, opts)
 	if err != nil {
 		return failPipelineCommand(stderr, commandState, terminalWriter, err)
diff --git a/internal/cli/run_contract_test.go b/internal/cli/run_contract_test.go
index 5522907..336a534 100644
--- a/internal/cli/run_contract_test.go
+++ b/internal/cli/run_contract_test.go
@@ -515,7 +515,7 @@ func TestRunSessionIDUsesEffectiveValueForPromptRequests(t *testing.T) {
 				}
 			}
 			harness := newStateTestHarness()
-			args := append([]string{"run", "sample", "--config", roots.config, "--input", roots.input, "--chunk_cache", "bypass"}, tt.args...)
+			args := append([]string{"run", "sample", "--config", roots.config, "--input", roots.input, "--chunk_cache", "bypass", "--debug"}, tt.args...)
 			var stdout, stderr bytes.Buffer
 			code := RunWithOptions(args, &stdout, &stderr, harness.options())
 			if code != 0 || stderr.Len() != 0 {
@@ -532,6 +532,11 @@ func TestRunSessionIDUsesEffectiveValueForPromptRequests(t *testing.T) {
 					t.Fatalf("session IDs = %#v, want %q", sessions, want)
 				}
 			}
+			var manifest artifacts.RunManifest
+			readStateTestSummaryJSON(t, onlyChildDir(t, roots.debug), "run-manifest.json", &manifest)
+			if session, ok := manifest.Metadata["session_id"]; !ok || session != want {
+				t.Fatalf("manifest session = %#v, want %q; metadata = %#v", session, want, manifest.Metadata)
+			}
 		})
 	}
 }
diff --git a/internal/cli/state_hardening_test.go b/internal/cli/state_hardening_test.go
index 137cacc..7c2c242 100644
--- a/internal/cli/state_hardening_test.go
+++ b/internal/cli/state_hardening_test.go
@@ -329,11 +329,25 @@ func TestRunUsesOneInjectedIdentityForDebugOutputAndManifest(t *testing.T) {
 	if manifest.StartedAt == nil || !manifest.StartedAt.Equal(wantStartedAt) {
 		t.Fatalf("manifest started at = %v, want %v", manifest.StartedAt, wantStartedAt)
 	}
+	rawInput, err := os.ReadFile(roots.input)
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantSessionID, err := resolvePromptSessionID("", "test/input", rawInput)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if sessionID, ok := manifest.Metadata["session_id"]; !ok || sessionID != wantSessionID {
+		t.Fatalf("manifest session = %#v, want %q; metadata = %#v", sessionID, wantSessionID, manifest.Metadata)
+	}
 	var invocation debugbundle.Invocation
 	readStateTestSummaryJSON(t, debugPath, "invocation.json", &invocation)
 	if invocation.RunID != runID || !invocation.StartedAt.Equal(wantStartedAt) {
 		t.Fatalf("debug invocation identity = %#v, want run %q at %v", invocation, runID, wantStartedAt)
 	}
+	if invocation.SessionID != wantSessionID {
+		t.Fatalf("debug invocation session = %q, want %q", invocation.SessionID, wantSessionID)
+	}
 	report := readStateTestRunReport(t, debugPath)
 	if !report.Succeeded || report.RunID != runID || report.PipelineID != "sample" || report.OutputPath != outputPath || report.DebugPath != debugPath || report.OutputCount != 1 || report.RejectedCount != 0 || report.WarningCount != 0 || report.ValidationStatus != "approved" {
 		t.Fatalf("success report = %#v", report)
@@ -343,6 +357,45 @@ func TestRunUsesOneInjectedIdentityForDebugOutputAndManifest(t *testing.T) {
 	}
 }
 
+func TestRunCheckpointReuseRequiresSameEffectiveSession(t *testing.T) {
+	roots := newStateTestRoots(t)
+	harness := newStateTestHarness()
+	run := func(extra ...string) stateTestResult {
+		args := []string{"run", "sample", "--config", roots.config, "--input", roots.input, "--chunk_cache", "bypass"}
+		args = append(args, extra...)
+		var stdout, stderr bytes.Buffer
+		return stateTestResult{code: RunWithOptions(args, &stdout, &stderr, harness.options()), stdout: stdout.String(), stderr: stderr.String()}
+	}
+
+	if result := run(); result.code != 0 {
+		t.Fatalf("initial run code=%d stdout=%q stderr=%q", result.code, result.stdout, result.stderr)
+	}
+	harness.mu.Lock()
+	initialExtractCalls := harness.extractCalls
+	harness.mu.Unlock()
+	if initialExtractCalls != 1 {
+		t.Fatalf("initial extract calls = %d, want 1", initialExtractCalls)
+	}
+	if result := run("--resume"); result.code != 0 {
+		t.Fatalf("same-session resume code=%d stdout=%q stderr=%q", result.code, result.stdout, result.stderr)
+	}
+	harness.mu.Lock()
+	reusedExtractCalls := harness.extractCalls
+	harness.mu.Unlock()
+	if reusedExtractCalls != initialExtractCalls {
+		t.Fatalf("extract calls after same-session resume = %d, want %d", reusedExtractCalls, initialExtractCalls)
+	}
+	if result := run("--resume", "--session-id", "different-session"); result.code != 0 {
+		t.Fatalf("different-session resume code=%d stdout=%q stderr=%q", result.code, result.stdout, result.stderr)
+	}
+	harness.mu.Lock()
+	differentSessionExtractCalls := harness.extractCalls
+	harness.mu.Unlock()
+	if differentSessionExtractCalls != initialExtractCalls+1 {
+		t.Fatalf("extract calls after different-session resume = %d, want %d", differentSessionExtractCalls, initialExtractCalls+1)
+	}
+}
+
 func TestRunWritesTerminalArtifactsForResolutionPipelineAndOutputFailures(t *testing.T) {
 	for _, tc := range []struct {
 		name             string
diff --git a/internal/core/debugbundle/bundle_test.go b/internal/core/debugbundle/bundle_test.go
index f4c0ce0..7906246 100644
--- a/internal/core/debugbundle/bundle_test.go
+++ b/internal/core/debugbundle/bundle_test.go
@@ -179,6 +179,30 @@ func TestWriteInvocationPreservesReasoningEffortOverrideStates(t *testing.T) {
 		})
 	}
 }
+
+func TestWriteInvocationOmitsEmptySessionID(t *testing.T) {
+	for _, sessionID := range []string{"", "session-123"} {
+		bundle, err := Allocate(t.TempDir(), testBundleRunID, time.Unix(0, 42))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := bundle.Summary().WriteInvocation(Invocation{Operation: "run", SessionID: sessionID}); err != nil {
+			t.Fatal(err)
+		}
+		data, err := os.ReadFile(filepath.Join(bundle.SummaryRoot(), ArtifactInvocationMetadata))
+		if err != nil {
+			t.Fatal(err)
+		}
+		var payload map[string]any
+		if err := json.Unmarshal(data, &payload); err != nil {
+			t.Fatal(err)
+		}
+		value, found := payload["session_id"]
+		if found != (sessionID != "") || (found && value != sessionID) {
+			t.Fatalf("session found=%t value=%#v, want found=%t value=%q; JSON=%s", found, value, sessionID != "", sessionID, data)
+		}
+	}
+}
 func TestSummaryWriterInternalWritesConfineArtifacts(t *testing.T) {
 	bundle, err := Allocate(t.TempDir(), testBundleRunID, time.Unix(0, 42))
 	if err != nil {
diff --git a/internal/core/debugbundle/summary.go b/internal/core/debugbundle/summary.go
index c937b0b..2ac8053 100644
--- a/internal/core/debugbundle/summary.go
+++ b/internal/core/debugbundle/summary.go
@@ -40,6 +40,7 @@ type Invocation struct {
 	OnlyLanes               []string  `json:"only_lanes,omitempty"`
 	ChunkCacheOverride      string    `json:"chunk_cache_override,omitempty"`
 	ReasoningEffortOverride *string   `json:"reasoning_effort_override,omitempty"`
+	SessionID               string    `json:"session_id,omitempty"`
 	RunID                   string    `json:"run_id"`
 	StartedAt               time.Time `json:"started_at"`
 }