diff --git a/backend/pkg/providers/providers.go b/backend/pkg/providers/providers.go
index a9a69c7d..b5d78463 100644
--- a/backend/pkg/providers/providers.go
+++ b/backend/pkg/providers/providers.go
@@ -5,6 +5,7 @@ import (
 	"crypto/rand"
 	"database/sql"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math"
 	"math/big"
@@ -317,7 +318,7 @@ func (pc *providerController) NewFlowProvider(
 		return nil, fmt.Errorf("failed to get primary docker image template: %w", err)
 	}
 
-	image, err := prv.Call(ctx, pconfig.OptionsTypeSimple, imageTmpl)
+	image, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, imageTmpl)
 	if err != nil {
 		return nil, fmt.Errorf("failed to select primary docker image via llm call: %w", err)
 	}
@@ -330,7 +331,7 @@ func (pc *providerController) NewFlowProvider(
 		return nil, fmt.Errorf("failed to get language template: %w", err)
 	}
 
-	language, err := prv.Call(ctx, pconfig.OptionsTypeSimple, languageTmpl)
+	language, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, languageTmpl)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get language: %w", err)
 	}
@@ -346,7 +347,7 @@ func (pc *providerController) NewFlowProvider(
 		return nil, fmt.Errorf("failed to get flow title template: %w", err)
 	}
 
-	title, err := prv.Call(ctx, pconfig.OptionsTypeSimple, titleTmpl)
+	title, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, titleTmpl)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get flow title: %w", err)
 	}
@@ -476,7 +477,7 @@ func (pc *providerController) NewAssistantProvider(
 		return nil, fmt.Errorf("failed to get language template: %w", err)
 	}
 
-	language, err := prv.Call(ctx, pconfig.OptionsTypeSimple, languageTmpl)
+	language, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, languageTmpl)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get language: %w", err)
 	}
@@ -492,7 +493,7 @@ func (pc *providerController) NewAssistantProvider(
 		return nil, fmt.Errorf("failed to get flow title template: %w", err)
 	}
 
-	title, err := prv.Call(ctx, pconfig.OptionsTypeSimple, titleTmpl)
+	title, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, titleTmpl)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get flow title: %w", err)
 	}
@@ -1079,3 +1080,44 @@ func newAtomicInt64(seed int64) *atomic.Int64 {
 	number.Store(seed)
 	return &number
 }
+
+// callWithSetupRetries wraps a single-shot LLM prompt call used during flow/
+// assistant bootstrap (docker image, language, and title selection) with the
+// same short retry-with-backoff already used for the agent execution loop
+// (see performSimpleChain/callWithRetries), so one transient error from the
+// LLM gateway (e.g. a bad gateway from a litellm proxy) does not fail flow or
+// assistant creation outright.
+func callWithSetupRetries(
+	ctx context.Context,
+	prv provider.Provider,
+	opt pconfig.ProviderOptionsType,
+	prompt string,
+) (string, error) {
+	var (
+		result string
+		err    error
+	)
+
+	for idx := 0; idx <= maxRetriesToCallSimpleChain; idx++ {
+		if idx == maxRetriesToCallSimpleChain {
+			return "", fmt.Errorf("failed to call llm after %d retries: %w", idx, err)
+		}
+
+		result, err = prv.Call(ctx, opt, prompt)
+		if err == nil {
+			return result, nil
+		}
+
+		if errors.Is(err, context.Canceled) {
+			return "", err
+		}
+
+		select {
+		case <-ctx.Done():
+			return "", ctx.Err()
+		case <-time.After(delayBetweenRetries):
+		}
+	}
+
+	return "", err
+}
diff --git a/backend/pkg/providers/providers_test.go b/backend/pkg/providers/providers_test.go
index f988363d..52491677 100644
--- a/backend/pkg/providers/providers_test.go
+++ b/backend/pkg/providers/providers_test.go
@@ -2,8 +2,11 @@ package providers
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"pentagi/pkg/config"
 	"pentagi/pkg/database"
@@ -224,3 +227,86 @@ func TestAgentConfigPricesMatchCatalog(t *testing.T) {
 		}
 	}
 }
+
+// fakeCallProvider overrides only Call(); embedding provider.Provider means
+// every other interface method is unimplemented and would panic on use,
+// which is fine since callWithSetupRetries only ever calls Call().
+type fakeCallProvider struct {
+	provider.Provider
+	callCount int
+	failTimes int
+	err       error
+	result    string
+}
+
+func (f *fakeCallProvider) Call(ctx context.Context, opt pconfig.ProviderOptionsType, prompt string) (string, error) {
+	f.callCount++
+	if f.callCount <= f.failTimes {
+		return "", f.err
+	}
+	return f.result, nil
+}
+
+func TestCallWithSetupRetries_SucceedsImmediately(t *testing.T) {
+	prv := &fakeCallProvider{result: "kali-linux"}
+
+	got, err := callWithSetupRetries(context.Background(), prv, pconfig.OptionsTypeSimple, "prompt")
+
+	require.NoError(t, err)
+	assert.Equal(t, "kali-linux", got)
+	assert.Equal(t, 1, prv.callCount, "a first-try success must not retry")
+}
+
+func TestCallWithSetupRetries_RetriesOnTransientErrorThenSucceeds(t *testing.T) {
+	// Exercises the real backoff once (a single delayBetweenRetries wait), so this
+	// test genuinely proves a transient 5xx from the LLM gateway self-heals
+	// instead of failing flow/assistant creation outright.
+	prv := &fakeCallProvider{
+		failTimes: 1,
+		err:       fmt.Errorf("API returned unexpected status code: 502: bad gateway"),
+		result:    "kali-linux",
+	}
+
+	got, err := callWithSetupRetries(context.Background(), prv, pconfig.OptionsTypeSimple, "prompt")
+
+	require.NoError(t, err)
+	assert.Equal(t, "kali-linux", got)
+	assert.Equal(t, 2, prv.callCount, "must retry exactly once after the transient failure")
+}
+
+func TestCallWithSetupRetries_ContextCanceledDuringWait_ReturnsWithoutFullBackoff(t *testing.T) {
+	prv := &fakeCallProvider{
+		failTimes: maxRetriesToCallSimpleChain, // always fails within the retry budget
+		err:       errors.New("connection refused"),
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		time.Sleep(20 * time.Millisecond)
+		cancel()
+	}()
+
+	start := time.Now()
+	_, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, "prompt")
+	elapsed := time.Since(start)
+
+	require.Error(t, err)
+	assert.ErrorIs(t, err, context.Canceled)
+	assert.Less(t, elapsed, delayBetweenRetries, "canceling context mid-wait must abort immediately, not wait out the full backoff")
+}
+
+func TestCallWithSetupRetries_ContextAlreadyCanceled_StopsWithoutRetrying(t *testing.T) {
+	prv := &fakeCallProvider{
+		failTimes: maxRetriesToCallSimpleChain,
+		err:       context.Canceled,
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	_, err := callWithSetupRetries(ctx, prv, pconfig.OptionsTypeSimple, "prompt")
+
+	require.Error(t, err)
+	assert.ErrorIs(t, err, context.Canceled)
+	assert.Equal(t, 1, prv.callCount, "a context.Canceled error from Call must stop retrying immediately")
+}
diff --git a/backend/pkg/templates/prompts/enricher.tmpl b/backend/pkg/templates/prompts/enricher.tmpl
index adceff6e..f7633391 100644
--- a/backend/pkg/templates/prompts/enricher.tmpl
+++ b/backend/pkg/templates/prompts/enricher.tmpl
@@ -171,7 +171,7 @@ Follow this prioritized approach to gather SUPPLEMENTARY information:
 <tool name="{{.GraphitiSearchToolName}}">
 <purpose>Search knowledge graph for episodic memory and execution history</purpose>
 <usage>Find what agents discovered and executed during operations</usage>
-<search_types>recent_context, episode_context, successful_tools, entity_relationships</search_types>
+<search_types>recent_context, episode_context, successful_tools, entity_relationships (only after another search type returns a node UUID; needs center_node_uuid)</search_types>
 </tool>
 {{- end}}
 
diff --git a/backend/pkg/templates/prompts/memorist.tmpl b/backend/pkg/templates/prompts/memorist.tmpl
index abe7602f..18993ee6 100644
--- a/backend/pkg/templates/prompts/memorist.tmpl
+++ b/backend/pkg/templates/prompts/memorist.tmpl
@@ -47,6 +47,12 @@ ALWAYS search Graphiti BEFORE searching vector database:
 - When asked about entities → Understand their relationships
 </when_to_search>
 
+<taxonomy_reference>
+node_labels (PascalCase singular, use verbatim): Host, Port, Service, WebApp, Endpoint, Account, Vulnerability, Misconfiguration, Capability, Credential, ValidAccess, PrivChange, Tool, ToolExecution, Artifact, Evidence, Attempt, AttackTechnique.
+edge_types (UPPER_SNAKE_CASE, use verbatim): HAS_PORT, RUNS_SERVICE, HOSTS_APP, HAS_ENDPOINT, DETECTED_VULNERABILITY (scanner hit, unverified) → CONFIRMED_VULNERABILITY (validated) → HAS_VULNERABILITY (exploited), HAS_MISCONFIGURATION, AUTHENTICATES_TO, YIELDED_ACCESS, ESCALATED_VIA, PIVOTED_TO, ATTEMPTED_ON.
+Never invent a label/edge outside this list; if unsure, omit node_labels/edge_types and rely on the free-text query instead.
+</taxonomy_reference>
+
 <search_type_selection>
 Choose the appropriate search type based on the information need:
 
@@ -70,15 +76,15 @@ Choose the appropriate search type based on the information need:
    - When: Looking for working command examples, successful approaches
    - Example: `search_type: "successful_tools", query: "successful nmap scans revealing services", min_mentions: 2`
 
-5. **entity_relationships** - Explore entity connections (requires entity UUID from prior search)
+5. **entity_relationships** - Explore entity connections (requires center_node_uuid from a prior search result; node_labels/edge_types are optional filters from the taxonomy reference above)
    - Use: "What is connected to [entity]?"
    - When: Understanding relationships between discovered entities
    - Example: `search_type: "entity_relationships", query: "related vulnerabilities and services", center_node_uuid: "[uuid]", max_depth: 2`
 
-6. **entity_by_label** - Type-specific inventory (requires specific labels from prior discovery)
+6. **entity_by_label** - Type-specific inventory using node_labels from the taxonomy reference above
    - Use: "List all [entity type] discovered"
    - When: Creating inventories, generating comprehensive reports
-   - Example: `search_type: "entity_by_label", query: "all discovered vulnerabilities", node_labels: ["VULNERABILITY"]`
+   - Example: `search_type: "entity_by_label", query: "all discovered vulnerabilities", node_labels: ["Vulnerability"]`
 
 7. **diverse_results** - Get varied perspectives and alternatives
    - Use: "What are different approaches/findings about [topic]?"
diff --git a/backend/pkg/templates/prompts/pentester.tmpl b/backend/pkg/templates/prompts/pentester.tmpl
index 685c3248..7404fc11 100644
--- a/backend/pkg/templates/prompts/pentester.tmpl
+++ b/backend/pkg/templates/prompts/pentester.tmpl
@@ -69,6 +69,12 @@ ALWAYS search Graphiti BEFORE attempting any significant action:
 - After discovering entities → Understand their relationships
 </when_to_search>
 
+<taxonomy_reference>
+node_labels (PascalCase singular, use verbatim): Host, Port, Service, WebApp, Endpoint, Account, Vulnerability, Misconfiguration, Capability, Credential, ValidAccess, PrivChange, Tool, ToolExecution, Artifact, Evidence, Attempt, AttackTechnique.
+edge_types (UPPER_SNAKE_CASE, use verbatim): HAS_PORT, RUNS_SERVICE, HOSTS_APP, HAS_ENDPOINT, DETECTED_VULNERABILITY (scanner hit, unverified) → CONFIRMED_VULNERABILITY (validated) → HAS_VULNERABILITY (exploited), HAS_MISCONFIGURATION, AUTHENTICATES_TO, YIELDED_ACCESS, ESCALATED_VIA, PIVOTED_TO, ATTEMPTED_ON.
+Never invent a label/edge outside this list; if unsure, omit node_labels/edge_types and rely on the free-text query instead.
+</taxonomy_reference>
+
 <search_type_selection>
 Choose the appropriate search type based on your need:
 
@@ -87,7 +93,7 @@ Choose the appropriate search type based on your need:
    - When: Need detailed context, understanding decision-making
    - Example: `search_type: "episode_context", query: "pentester agent analysis of SSH vulnerability"`
 
-4. **entity_relationships** - Explore entity connections (can only be used after discovering an entity using other search types)
+4. **entity_relationships** - Explore entity connections (requires center_node_uuid from a prior search result; node_labels/edge_types are optional filters from the taxonomy reference above)
    - Use: "What services/vulnerabilities are related to [entity]?"
    - When: Investigating a specific IP, service, or vulnerability
    - Example: `search_type: "entity_relationships", query: "services and vulnerabilities", center_node_uuid: "[uuid]", max_depth: 2`
@@ -97,10 +103,10 @@ Choose the appropriate search type based on your need:
    - When: Current approach failing, need alternatives
    - Example: `search_type: "diverse_results", query: "privilege escalation techniques on Linux", diversity_level: "high"`
 
-6. **entity_by_label** - Type-specific inventory (can only be used after discovering an entity using other search types, never use generic Entity label — only use specific labels like TechnicalFinding, Tool, AttackTechnique, etc.)
+6. **entity_by_label** - Type-specific inventory using node_labels from the taxonomy reference above — never a generic "Entity" label
    - Use: "List all [entity type] we've discovered"
    - When: Building inventories, generating reports
-   - Example: `search_type: "entity_by_label", query: "all discovered vulnerabilities", node_labels: ["VULNERABILITY"]`
+   - Example: `search_type: "entity_by_label", query: "all discovered vulnerabilities", node_labels: ["Vulnerability"]`
 </search_type_selection>
 
 <query_construction>
diff --git a/backend/pkg/tools/args.go b/backend/pkg/tools/args.go
index ed018716..6618d679 100644
--- a/backend/pkg/tools/args.go
+++ b/backend/pkg/tools/args.go
@@ -159,15 +159,15 @@ type WebSearchAction struct {
 }
 
 type GraphitiSearchAction struct {
-	SearchType     String   `json:"search_type" jsonschema:"required,type=string,enum=temporal_window,enum=entity_relationships,enum=diverse_results,enum=episode_context,enum=successful_tools,enum=recent_context,enum=entity_by_label" jsonschema_description:"Type of search to perform: temporal_window (time-bounded search), entity_relationships (graph traversal from an entity), diverse_results (anti-redundancy search), episode_context (full agent reasoning and tool outputs), successful_tools (proven techniques), recent_context (latest findings), entity_by_label (type-specific entity search)"`
+	SearchType     String   `json:"search_type" jsonschema:"required,type=string,enum=temporal_window,enum=entity_relationships,enum=diverse_results,enum=episode_context,enum=successful_tools,enum=recent_context,enum=entity_by_label" jsonschema_description:"Type of search to perform: temporal_window (time-bounded search), entity_relationships (graph traversal from an entity), diverse_results (anti-redundancy search), episode_context (full agent reasoning and tool outputs), successful_tools (proven techniques), recent_context (latest findings), entity_by_label (type-specific entity search, REQUIRES node_labels)"`
 	Query          string   `json:"query" jsonschema:"required" jsonschema_description:"Technical-channel payload — natural language query against the team's temporal knowledge graph. ALWAYS written in English regardless of the engagement language: the graph is indexed in English and shared across all engagements; non-English queries will fail to retrieve stored episodic memory."`
 	MaxResults     *Int64   `json:"max_results,omitempty" jsonschema:"title=Maximum Results,type=integer" jsonschema_description:"Maximum number of results to return (default varies by search type)"`
 	TimeStart      string   `json:"time_start,omitempty" jsonschema_description:"Start of time window (ISO 8601 format, required for temporal_window)"`
 	TimeEnd        string   `json:"time_end,omitempty" jsonschema_description:"End of time window (ISO 8601 format, required for temporal_window)"`
 	CenterNodeUUID string   `json:"center_node_uuid,omitempty" jsonschema_description:"UUID of entity to search from (required for entity_relationships)"`
 	MaxDepth       *Int64   `json:"max_depth,omitempty" jsonschema:"title=Maximum Depth,type=integer" jsonschema_description:"Maximum graph traversal depth (default: 2, max: 3, for entity_relationships)"`
-	NodeLabels     []string `json:"node_labels,omitempty" jsonschema_description:"Filter to specific node types (e.g., ['IP_ADDRESS', 'SERVICE', 'VULNERABILITY'])"`
-	EdgeTypes      []string `json:"edge_types,omitempty" jsonschema_description:"Filter to specific relationship types (e.g., ['HAS_PORT', 'EXPLOITS'])"`
+	NodeLabels     []string `json:"node_labels,omitempty" jsonschema_description:"Filter to specific node types — EXACT taxonomy names, PascalCase singular (e.g., ['Host', 'Service', 'Vulnerability']). REQUIRED (non-empty) when search_type is entity_by_label; optional filter otherwise"`
+	EdgeTypes      []string `json:"edge_types,omitempty" jsonschema_description:"Filter to specific relationship types — EXACT taxonomy names, UPPER_SNAKE_CASE (e.g., ['HAS_PORT', 'HAS_VULNERABILITY'])"`
 	DiversityLevel String   `json:"diversity_level,omitempty" jsonschema:"type=string,enum=low,enum=medium,enum=high" jsonschema_description:"How much diversity to prioritize (default: medium, for diverse_results)"`
 	MinMentions    *Int64   `json:"min_mentions,omitempty" jsonschema:"title=Minimum Mentions,type=integer" jsonschema_description:"Minimum episode mentions (default: 2, for successful_tools)"`
 	RecencyWindow  String   `json:"recency_window,omitempty" jsonschema:"type=string,enum=1h,enum=6h,enum=24h,enum=7d" jsonschema_description:"How far back to search (default: 24h, for recent_context)"`
diff --git a/backend/pkg/tools/browser.go b/backend/pkg/tools/browser.go
index 3bc368b5..4f5f7f31 100644
--- a/backend/pkg/tools/browser.go
+++ b/backend/pkg/tools/browser.go
@@ -22,9 +22,10 @@ import (
 )
 
 const (
-	minMdContentSize   = 50
-	minHtmlContentSize = 300
-	minImgContentSize  = 2048
+	minMdContentSize         = 50
+	minHtmlContentSize       = 300
+	minImgContentSize        = 2048
+	maxScraperErrorBodyBytes = 512
 )
 
 // nonHTMLExtensions lists URL path suffixes that point to resources the scraper
@@ -511,6 +512,17 @@ func (b *browser) callScraper(url string) ([]byte, error) {
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
+		if resp.StatusCode >= 500 {
+			body, _ := io.ReadAll(io.LimitReader(resp.Body, maxScraperErrorBodyBytes+1))
+			if preview := strings.TrimSpace(string(body)); preview != "" {
+				if truncated := len(body) > maxScraperErrorBodyBytes; truncated {
+					preview = preview[:maxScraperErrorBodyBytes] + "... [truncated]"
+				}
+				return nil, fmt.Errorf(
+					"unexpected resp code for scraper '%s': %d, response: %s", url, resp.StatusCode, preview,
+				)
+			}
+		}
 		return nil, fmt.Errorf("unexpected resp code for scraper '%s': %d", url, resp.StatusCode)
 	}
 
diff --git a/backend/pkg/tools/browser_test.go b/backend/pkg/tools/browser_test.go
index 0075ff90..92da6b42 100644
--- a/backend/pkg/tools/browser_test.go
+++ b/backend/pkg/tools/browser_test.go
@@ -413,6 +413,73 @@ func TestGetHTML_EmptyContent_ReturnsError(t *testing.T) {
 	}
 }
 
+func TestCallScraper_ServerError5xx_IncludesBodyPreview(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadGateway)
+		fmt.Fprint(w, "<html><body>502 Bad Gateway</body></html>")
+	}))
+	defer ts.Close()
+
+	b := &browser{flowID: 1}
+
+	_, err := b.callScraper(ts.URL)
+	if err == nil {
+		t.Fatal("callScraper() should error on 5xx response")
+	}
+	if !strings.Contains(err.Error(), "502") {
+		t.Errorf("callScraper() error should mention the status code, got: %v", err)
+	}
+	if !strings.Contains(err.Error(), "502 Bad Gateway") {
+		t.Errorf("callScraper() error should include the response body, got: %v", err)
+	}
+}
+
+func TestCallScraper_ServerError5xx_BodyTruncatedAt1024Bytes(t *testing.T) {
+	hugeBody := strings.Repeat("x", 2000)
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+		fmt.Fprint(w, hugeBody)
+	}))
+	defer ts.Close()
+
+	b := &browser{flowID: 1}
+
+	_, err := b.callScraper(ts.URL)
+	if err == nil {
+		t.Fatal("callScraper() should error on 5xx response")
+	}
+	if strings.Count(err.Error(), "x") >= 2000 {
+		t.Fatalf("expected the 2000-byte body to be truncated to the 1024-byte cap, got error of length %d", len(err.Error()))
+	}
+	if !strings.Contains(err.Error(), "truncated") {
+		t.Errorf("callScraper() error should indicate truncation, got: %v", err)
+	}
+}
+
+func TestCallScraper_ClientError4xx_NoBodyPreview(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		fmt.Fprint(w, "not found body")
+	}))
+	defer ts.Close()
+
+	b := &browser{flowID: 1}
+
+	_, err := b.callScraper(ts.URL)
+	if err == nil {
+		t.Fatal("callScraper() should error on 4xx response")
+	}
+	if !strings.Contains(err.Error(), "404") {
+		t.Errorf("callScraper() error should mention the status code, got: %v", err)
+	}
+	// 4xx means our own request was malformed, not the scraper backend failing,
+	// so the body preview (only meaningful for 5xx) must not be included.
+	if strings.Contains(err.Error(), "not found body") {
+		t.Errorf("callScraper() error should not include the response body for 4xx, got: %v", err)
+	}
+}
+
 func TestGetHTML_BinaryURL_ReturnsError(t *testing.T) {
 	b := &browser{flowID: 1, scPubURL: "http://127.0.0.1:1"}
 
diff --git a/backend/pkg/tools/graphiti_search.go b/backend/pkg/tools/graphiti_search.go
index 99f048e2..8dc10d9c 100644
--- a/backend/pkg/tools/graphiti_search.go
+++ b/backend/pkg/tools/graphiti_search.go
@@ -15,6 +15,7 @@ import (
 	obs "pentagi/pkg/observability"
 	"pentagi/pkg/observability/langfuse"
 
+	"github.com/google/uuid"
 	"github.com/sirupsen/logrus"
 )
 
@@ -361,6 +362,12 @@ func (t *graphitiSearchTool) handleEntityRelationshipsSearch(
 	if args.CenterNodeUUID == "" {
 		return "", fmt.Errorf("center_node_uuid is required for entity_relationships search")
 	}
+	if _, err := uuid.Parse(args.CenterNodeUUID); err != nil {
+		return "", fmt.Errorf(
+			"center_node_uuid must be a valid UUID copied verbatim from the 'UUID:' field of a prior "+
+				"graphiti_search result, got %q", args.CenterNodeUUID,
+		)
+	}
 
 	maxResults := args.MaxResults.Int()
 	if maxResults <= 0 {
@@ -544,7 +551,10 @@ func (t *graphitiSearchTool) handleEntityByLabelSearch(
 	observationObject *graphiti.Observation,
 ) (string, error) {
 	if len(args.NodeLabels) == 0 {
-		return "", fmt.Errorf("node_labels is required for entity_by_label search")
+		return "", fmt.Errorf(
+			"node_labels is required for entity_by_label search: pass one or more EXACT taxonomy node names " +
+				`(PascalCase singular), e.g. node_labels: ["Host", "Service", "Vulnerability"]`,
+		)
 	}
 
 	maxResults := args.MaxResults.Int()
diff --git a/backend/pkg/tools/graphiti_search_test.go b/backend/pkg/tools/graphiti_search_test.go
index 9b47b8a6..4001ac34 100644
--- a/backend/pkg/tools/graphiti_search_test.go
+++ b/backend/pkg/tools/graphiti_search_test.go
@@ -29,7 +29,10 @@ func (s *stubGraphitiSearcher) TemporalWindowSearch(
 func (s *stubGraphitiSearcher) EntityRelationshipsSearch(
 	ctx context.Context, req graphiti.EntityRelationshipSearchRequest,
 ) (*graphiti.EntityRelationshipSearchResponse, error) {
-	return nil, s.err
+	if s.err != nil {
+		return nil, s.err
+	}
+	return &graphiti.EntityRelationshipSearchResponse{}, nil
 }
 
 func (s *stubGraphitiSearcher) DiverseResultsSearch(
@@ -59,7 +62,10 @@ func (s *stubGraphitiSearcher) RecentContextSearch(
 func (s *stubGraphitiSearcher) EntityByLabelSearch(
 	ctx context.Context, req graphiti.EntityByLabelSearchRequest,
 ) (*graphiti.EntityByLabelSearchResponse, error) {
-	return nil, s.err
+	if s.err != nil {
+		return nil, s.err
+	}
+	return &graphiti.EntityByLabelSearchResponse{}, nil
 }
 
 // fakeNetError mimics the *url.Error shape produced by http.Client.Do on a
@@ -175,6 +181,76 @@ func TestGraphitiSearchTool_Handle_ValidationError_StaysHard(t *testing.T) {
 	}
 }
 
+func TestGraphitiSearchTool_Handle_EntityByLabel_MissingNodeLabels_GivesActionableError(t *testing.T) {
+	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})
+
+	args := []byte(`{"search_type":"entity_by_label","query":"test query","message":"m"}`)
+	_, err := tool.Handle(t.Context(), GraphitiSearchToolName, args)
+
+	if err == nil {
+		t.Fatal("expected a hard failure when node_labels is missing for entity_by_label, got nil error")
+	}
+	if !strings.Contains(err.Error(), "node_labels is required") {
+		t.Fatalf("expected error to state node_labels is required, got: %v", err)
+	}
+	if !strings.Contains(err.Error(), "Vulnerability") {
+		t.Fatalf("expected error to include a real taxonomy example value to guide the LLM, got: %v", err)
+	}
+}
+
+func TestGraphitiSearchTool_Handle_EntityByLabel_WithNodeLabels_Succeeds(t *testing.T) {
+	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})
+
+	args := []byte(`{"search_type":"entity_by_label","query":"test query","node_labels":["Vulnerability"],"message":"m"}`)
+	_, err := tool.Handle(t.Context(), GraphitiSearchToolName, args)
+
+	if err != nil {
+		t.Fatalf("expected no error when node_labels is present, got: %v", err)
+	}
+}
+
+func TestGraphitiSearchTool_Handle_EntityRelationships_MissingCenterNodeUUID_StaysHard(t *testing.T) {
+	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})
+
+	args := []byte(`{"search_type":"entity_relationships","query":"test query","message":"m"}`)
+	_, err := tool.Handle(t.Context(), GraphitiSearchToolName, args)
+
+	if err == nil || !strings.Contains(err.Error(), "center_node_uuid is required") {
+		t.Fatalf("expected hard 'center_node_uuid is required' error, got: %v", err)
+	}
+}
+
+func TestGraphitiSearchTool_Handle_EntityRelationships_MalformedCenterNodeUUID_GivesActionableError(t *testing.T) {
+	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})
+
+	// Simulates a diagnostic string, truncated ID, or otherwise non-UUID value
+	// ending up in center_node_uuid (e.g. a hallucinated or mangled value) -
+	// this must be rejected before ever reaching the graph backend.
+	args := []byte(`{"search_type":"entity_relationships","query":"test query","center_node_uuid":"not-a-real-uuid","message":"m"}`)
+	_, err := tool.Handle(t.Context(), GraphitiSearchToolName, args)
+
+	if err == nil {
+		t.Fatal("expected a hard failure for a malformed center_node_uuid, got nil error")
+	}
+	if !strings.Contains(err.Error(), "must be a valid UUID") {
+		t.Fatalf("expected error to explain the UUID requirement, got: %v", err)
+	}
+	if !strings.Contains(err.Error(), "not-a-real-uuid") {
+		t.Fatalf("expected error to echo back the offending value, got: %v", err)
+	}
+}
+
+func TestGraphitiSearchTool_Handle_EntityRelationships_ValidCenterNodeUUID_Succeeds(t *testing.T) {
+	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})
+
+	args := []byte(`{"search_type":"entity_relationships","query":"test query","center_node_uuid":"f7b95dfc-ee58-4a8b-8d85-582cf117b4df","message":"m"}`)
+	_, err := tool.Handle(t.Context(), GraphitiSearchToolName, args)
+
+	if err != nil {
+		t.Fatalf("expected no error for a well-formed center_node_uuid, got: %v", err)
+	}
+}
+
 func TestGraphitiSearchTool_Handle_InvalidRecencyWindow_StaysHard(t *testing.T) {
 	tool := NewGraphitiSearchTool(1, nil, nil, &stubGraphitiSearcher{enabled: true})