[Phase 2.1] Synthesis workflow definition (#12)

## Changes
- `workflow/synthesis.go` — 5-stage synthesis pipeline as Temporal workflow
- `workflow/synthesis_test.go` — 5 tests using Temporal test framework

## Pipeline Stages
1. **ChunkAndEmbed** — chunk text + generate embeddings
2. **ExtractEntities** — LLM entity extraction with reflection
3. **ExtractFacts** — pattern + LLM fact extraction
4. **DetectContradictions** — pre-filter + LLM verification
5. **PersistSynthesis** — save all results to DB

workflow/synthesis_test.go

@@ -0,0 +1,179 @@
+package workflow
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"go.temporal.io/sdk/testsuite"
+)
+
+// Stub activity functions for test registration
+func ChunkAndEmbedActivity(_ context.Context, _ SynthesisInput) (string, error) { return "", nil }
+func ExtractEntitiesActivity(_ context.Context, _ string, _ string) ([]ExtractedEntity, error) { return nil, nil }
+func ExtractFactsActivity(_ context.Context, _ string, _ string, _ []ExtractedEntity) ([]ExtractedFact, error) { return nil, nil }
+func DetectContradictionsActivity(_ context.Context, _ string, _ []ExtractedFact) ([]ContradictionResult, error) { return nil, nil }
+func PersistSynthesisActivity(_ context.Context, _ PersistInput) error { return nil }
+
+func registerSynthesisActivities(env *testsuite.TestWorkflowEnvironment) {
+	env.RegisterActivity(ChunkAndEmbedActivity)
+	env.RegisterActivity(ExtractEntitiesActivity)
+	env.RegisterActivity(ExtractFactsActivity)
+	env.RegisterActivity(DetectContradictionsActivity)
+	env.RegisterActivity(PersistSynthesisActivity)
+}
+
+func TestSynthesisWorkflow_Success(t *testing.T) {
+	ts := &testsuite.WorkflowTestSuite{}
+	env := ts.NewTestWorkflowEnvironment()
+
+	input := SynthesisInput{
+		Project: "poimen",
+		Source:  "transcript://test-123",
+		Text:    "Kubernetes uses port 8080 for the API server",
+		Kind:    "L1",
+	}
+
+	registerSynthesisActivities(env)
+
+	// Stage 1: Chunk + Embed
+	env.OnActivity(ChunkAndEmbedActivity, mock.Anything, input).Return("chunk-abc123", nil)
+
+	// Stage 2: Entity Extraction
+	entities := []ExtractedEntity{
+		{Name: "Kubernetes", EntityType: "tool", Confidence: 0.95},
+		{Name: "API server", EntityType: "component", Confidence: 0.90},
+	}
+	env.OnActivity(ExtractEntitiesActivity, mock.Anything, "chunk-abc123", input.Text).Return(entities, nil)
+
+	// Stage 3: Fact Extraction
+	facts := []ExtractedFact{
+		{Subject: "Kubernetes", Predicate: "uses_port", Object: "8080", Confidence: 0.85},
+	}
+	env.OnActivity(ExtractFactsActivity, mock.Anything, "chunk-abc123", input.Text, entities).Return(facts, nil)
+
+	// Stage 4: Contradiction Detection
+	contradictions := []ContradictionResult{}
+	env.OnActivity(DetectContradictionsActivity, mock.Anything, "poimen", facts).Return(contradictions, nil)
+
+	// Stage 5: Persist
+	env.OnActivity(PersistSynthesisActivity, mock.Anything, mock.Anything).Return(nil)
+
+	env.ExecuteWorkflow(SynthesisWorkflow, input)
+
+	assert.True(t, env.IsWorkflowCompleted())
+	assert.NoError(t, env.GetWorkflowError())
+
+	var result SynthesisResult
+	assert.NoError(t, env.GetWorkflowResult(&result))
+	assert.Equal(t, "chunk-abc123", result.ChunkID)
+	assert.Equal(t, 2, result.EntitiesExtracted)
+	assert.Equal(t, 1, result.FactsExtracted)
+	assert.Equal(t, 0, result.Contradictions)
+	assert.Equal(t, 0, result.ReviewQueued)
+}
+
+func TestSynthesisWorkflow_WithContradictions(t *testing.T) {
+	ts := &testsuite.WorkflowTestSuite{}
+	env := ts.NewTestWorkflowEnvironment()
+	registerSynthesisActivities(env)
+
+	input := SynthesisInput{
+		Project: "poimen",
+		Source:  "transcript://test-456",
+		Text:    "Port 8080 is used by nginx",
+		Kind:    "L1",
+	}
+
+	env.OnActivity(ChunkAndEmbedActivity, mock.Anything, input).Return("chunk-def456", nil)
+
+	entities := []ExtractedEntity{
+		{Name: "nginx", EntityType: "tool", Confidence: 0.92},
+	}
+	env.OnActivity(ExtractEntitiesActivity, mock.Anything, "chunk-def456", input.Text).Return(entities, nil)
+
+	facts := []ExtractedFact{
+		{Subject: "nginx", Predicate: "uses_port", Object: "8080", Confidence: 0.88},
+	}
+	env.OnActivity(ExtractFactsActivity, mock.Anything, "chunk-def456", input.Text, entities).Return(facts, nil)
+
+	contradictions := []ContradictionResult{
+		{
+			FactA:        ExtractedFact{Subject: "Kubernetes", Predicate: "uses_port", Object: "8080"},
+			FactB:        ExtractedFact{Subject: "nginx", Predicate: "uses_port", Object: "8080"},
+			Severity:     "medium",
+			AutoResolved: false,
+			QueuedReview: true,
+		},
+	}
+	env.OnActivity(DetectContradictionsActivity, mock.Anything, "poimen", facts).Return(contradictions, nil)
+	env.OnActivity(PersistSynthesisActivity, mock.Anything, mock.Anything).Return(nil)
+
+	env.ExecuteWorkflow(SynthesisWorkflow, input)
+
+	assert.True(t, env.IsWorkflowCompleted())
+	assert.NoError(t, env.GetWorkflowError())
+
+	var result SynthesisResult
+	assert.NoError(t, env.GetWorkflowResult(&result))
+	assert.Equal(t, 1, result.Contradictions)
+	assert.Equal(t, 1, result.ReviewQueued)
+}
+
+func TestSynthesisWorkflow_EntityExtractionFails(t *testing.T) {
+	ts := &testsuite.WorkflowTestSuite{}
+	env := ts.NewTestWorkflowEnvironment()
+	registerSynthesisActivities(env)
+
+	input := SynthesisInput{
+		Project: "poimen",
+		Source:  "transcript://test-789",
+		Text:    "Some text",
+		Kind:    "L1",
+	}
+
+	env.OnActivity(ChunkAndEmbedActivity, mock.Anything, input).Return("chunk-xyz", nil)
+	env.OnActivity(ExtractEntitiesActivity, mock.Anything, "chunk-xyz", input.Text).
+		Return(nil, assert.AnError)
+
+	env.ExecuteWorkflow(SynthesisWorkflow, input)
+
+	assert.True(t, env.IsWorkflowCompleted())
+	assert.Error(t, env.GetWorkflowError())
+	assert.Contains(t, env.GetWorkflowError().Error(), "stage 2 entity extraction")
+}
+
+func TestSynthesisWorkflow_ChunkFails(t *testing.T) {
+	ts := &testsuite.WorkflowTestSuite{}
+	env := ts.NewTestWorkflowEnvironment()
+	registerSynthesisActivities(env)
+
+	input := SynthesisInput{
+		Project: "poimen",
+		Source:  "transcript://test-fail",
+		Text:    "Bad text",
+		Kind:    "L1",
+	}
+
+	env.OnActivity(ChunkAndEmbedActivity, mock.Anything, input).Return("", assert.AnError)
+
+	env.ExecuteWorkflow(SynthesisWorkflow, input)
+
+	assert.True(t, env.IsWorkflowCompleted())
+	assert.Error(t, env.GetWorkflowError())
+	assert.Contains(t, env.GetWorkflowError().Error(), "stage 1 chunk+embed")
+}
+
+func TestSynthesisInput_Fields(t *testing.T) {
+	input := SynthesisInput{
+		Project: "test",
+		Source:  "source://1",
+		Text:    "hello",
+		Kind:    "L2",
+		Tags:    []string{"tag1", "tag2"},
+	}
+	assert.Equal(t, "test", input.Project)
+	assert.Equal(t, "L2", input.Kind)
+	assert.Len(t, input.Tags, 2)
+}