diff --git a/internal/server/manager.go b/internal/server/manager.go
index 45ac851a..c1497907 100644
--- a/internal/server/manager.go
+++ b/internal/server/manager.go
@@ -541,6 +541,7 @@ func (i *Investigation) Start() error {
 		LinkedRepos:            i.LinkedRepos,
 		LaunchCwd:              i.LaunchCwd,
 		KubeconfigPath:         i.KubeconfigPath,
+		Cluster:                i.ActiveContext,
 		Profile:                i.Profile,
 	})
 	if err != nil {
diff --git a/internal/server/rehydrate.go b/internal/server/rehydrate.go
index 7e7f2c96..895203a1 100644
--- a/internal/server/rehydrate.go
+++ b/internal/server/rehydrate.go
@@ -141,6 +141,7 @@ func (a *apiHandlers) rehydrate(inv *Investigation) error {
 		LinkedRepos:            linked,
 		LaunchCwd:              inv.LaunchCwd,
 		KubeconfigPath:         inv.KubeconfigPath,
+		Cluster:                inv.ActiveContext,
 		Profile:                a.prof,
 	}
 	priorID := inv.ClaudeSessionID
diff --git a/internal/sessions/session.go b/internal/sessions/session.go
index 8d9e5925..beb7cab4 100644
--- a/internal/sessions/session.go
+++ b/internal/sessions/session.go
@@ -23,13 +23,13 @@ import (
 // Options describes how to launch one session. They mirror the bits of
 // preflight.Result and program-level Deps that affect what claude sees.
 type Options struct {
-	Namespace        string
-	UserNotes        string
-	IncidentURL      string // operator-supplied incident.io incident URL; empty when not set
-	SlackChannelURL  string // operator-supplied slack channel/thread URL; empty when not set
-	SlackChannelID   string
-	SlackChannelName string
-	MCPConfigPath    string
+	Namespace              string
+	UserNotes              string
+	IncidentURL            string // operator-supplied incident.io incident URL; empty when not set
+	SlackChannelURL        string // operator-supplied slack channel/thread URL; empty when not set
+	SlackChannelID         string
+	SlackChannelName       string
+	MCPConfigPath          string
 	SlackMCPAvailable      bool // triagent-slack MCP wired (slack token linked)
 	IncidentioMCPAvailable bool // triagent-incidentio MCP wired (incidentio token linked)
 	LinkedRepos            []repos.LinkedRepo
@@ -51,7 +51,9 @@ type Options struct {
 	AlertKind string
 	// ProjectID is the deployment / tenant identifier (when known).
 	ProjectID string
-	// Cluster is the kube-context / cluster name (when known).
+	// Cluster is the kubeconfig context name the launcher seeded at
+	// preflight (when known). Rendered as kubernetes-context in the
+	// opening prompt and exposed to namespace_derivation as "cluster".
 	Cluster string
 }
 
@@ -184,9 +186,17 @@ func clusterIDFromNamespace(ns string) string {
 // from Options. Events are delivered on the returned channel; the channel
 // closes when claude exits or ctx is cancelled.
 func (s *Session) Start(ctx context.Context) (<-chan claude.Event, error) {
+	return s.inner.Start(ctx, s.startPrompt())
+}
+
+// startPrompt renders the opening prompt from Options. Cluster feeds the
+// Environment block's kubernetes-context line so the agent sees the
+// context the launcher already seeded instead of "<unset>".
+func (s *Session) startPrompt() string {
 	clusterID := clusterIDFromNamespace(s.opts.Namespace)
-	prompt := prompts.Build(prompts.Env{
-		UserNotes:              s.opts.UserNotes,
+	return prompts.Build(prompts.Env{
+		Context:   s.opts.Cluster,
+		UserNotes: s.opts.UserNotes,
 		InputValues: map[string]map[string]any{
 			"cluster_id":    {"value": clusterID},
 			"incident_url":  {"value": s.opts.IncidentURL},
@@ -197,7 +207,6 @@ func (s *Session) Start(ctx context.Context) (<-chan claude.Event, error) {
 		IncidentioMCPAvailable: s.opts.IncidentioMCPAvailable,
 		LinkedRepos:            s.opts.LinkedRepos,
 	}, s.opts.Profile)
-	return s.inner.Start(ctx, prompt)
 }
 
 // Resume continues the most-recent conversation with a follow-up prompt.
diff --git a/internal/sessions/session_test.go b/internal/sessions/session_test.go
index 7fab1f2b..75a48deb 100644
--- a/internal/sessions/session_test.go
+++ b/internal/sessions/session_test.go
@@ -139,3 +139,20 @@ func TestNew_ForwardsProfileInvestigationModel(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "claude-opus-4-7", sess.inner.Model())
 }
+
+func TestStartPrompt_EmitsSeededKubeContext(t *testing.T) {
+	t.Parallel()
+	s := &Session{opts: Options{
+		Cluster: "camunda.teleport.sh-saas-int-worker-3",
+		Profile: &profile.Profile{},
+	}}
+	got := s.startPrompt()
+	assert.Contains(t, got, "kubernetes-context: camunda.teleport.sh-saas-int-worker-3\n")
+	assert.NotContains(t, got, "kubernetes-context: <unset>")
+}
+
+func TestStartPrompt_UnsetWhenNoContextSeeded(t *testing.T) {
+	t.Parallel()
+	s := &Session{opts: Options{Profile: &profile.Profile{}}}
+	assert.Contains(t, s.startPrompt(), "kubernetes-context: <unset>\n")
+}