diff --git a/cmd/antidriftd/main.go b/cmd/antidriftd/main.go
index 7a81b04..ef29757 100644
--- a/cmd/antidriftd/main.go
+++ b/cmd/antidriftd/main.go
@@ -12,6 +12,7 @@ import (
 
 	"antidrift/internal/ai"
 	"antidrift/internal/evidence"
+	"antidrift/internal/knowledge"
 	"antidrift/internal/session"
 	"antidrift/internal/statusfile"
 	"antidrift/internal/store"
@@ -54,6 +55,13 @@ func main() {
 	ctrl.SetTasks(tasks.NewMarvin(os.Getenv("ANTIDRIFT_MARVIN_CMD")))
 	log.Printf("tasks: marvin adapter (am)")
 
+	// Wire the Knowledge port: a single profile file grounding the coach. The
+	// default path is overridable with ANTIDRIFT_KNOWLEDGE_FILE; unset falls back
+	// to ~/.antidrift/knowledge.md. A missing/unreadable file degrades to an
+	// ungrounded coach at load time — planning still works.
+	ctrl.SetKnowledge(knowledge.NewFileSource(os.Getenv("ANTIDRIFT_KNOWLEDGE_FILE")))
+	log.Printf("knowledge: file adapter")
+
 	// Mirror runtime status to ~/.antidrift_status for a window-manager bar.
 	// A misconfigured home dir degrades to no status file, not a failed start.
 	if statusPath, err := statusfile.DefaultPath(); err != nil {
diff --git a/internal/web/web.go b/internal/web/web.go
index f887b23..1a5a207 100644
--- a/internal/web/web.go
+++ b/internal/web/web.go
@@ -58,6 +58,7 @@ func (s *Server) Router() *gin.Engine {
 	r.POST("/end", s.handleEnd)
 	r.POST("/refocus", s.handleRefocus)
 	r.POST("/ontask", s.handleOnTask)
+	r.POST("/knowledge/path", s.handleKnowledgePath)
 	return r
 }
 
@@ -124,6 +125,24 @@ func (s *Server) handleCommitment(c *gin.Context) {
 	s.respond(c, err)
 }
 
+type knowledgePathRequest struct {
+	Path string `json:"path"`
+}
+
+// handleKnowledgePath repoints the profile file at runtime (session-only). It
+// mutates config, not commitment state, so it never returns a transition error;
+// it just sets the path, re-loads, and broadcasts the refreshed state.
+func (s *Server) handleKnowledgePath(c *gin.Context) {
+	var req knowledgePathRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid json"})
+		return
+	}
+	s.ctrl.SetKnowledgePath(req.Path)
+	s.broadcast()
+	c.Data(http.StatusOK, "application/json", []byte(s.stateJSON()))
+}
+
 func (s *Server) handleComplete(c *gin.Context) {
 	s.cancelExpiry()
 	s.respond(c, s.ctrl.Complete())
diff --git a/internal/web/web_test.go b/internal/web/web_test.go
index da9049a..b99ae81 100644
--- a/internal/web/web_test.go
+++ b/internal/web/web_test.go
@@ -12,6 +12,7 @@ import (
 	"antidrift/internal/ai"
 	"antidrift/internal/domain"
 	"antidrift/internal/evidence"
+	"antidrift/internal/knowledge"
 	"antidrift/internal/session"
 	"antidrift/internal/tasks"
 
@@ -108,7 +109,7 @@ type stubCoach struct {
 	err  error
 }
 
-func (s stubCoach) Coach(ctx context.Context, intent string) (ai.Proposal, error) {
+func (s stubCoach) Coach(ctx context.Context, intent, grounding string) (ai.Proposal, error) {
 	return s.prop, s.err
 }
 
@@ -281,3 +282,57 @@ func TestCommitmentCarriesAllowedClassesAndRoutesWork(t *testing.T) {
 		t.Fatalf("refocus while Active: want 200, got %d", w.Code)
 	}
 }
+
+type stubSource struct {
+	profile knowledge.Profile
+}
+
+func (s stubSource) Load(ctx context.Context, path string) (knowledge.Profile, error) {
+	if path != "" {
+		return knowledge.Profile{Text: "from " + path, Path: path}, nil
+	}
+	return s.profile, nil
+}
+
+func TestPlanningStatePayloadCarriesKnowledge(t *testing.T) {
+	s := newTestServer(t)
+	s.ctrl.SetKnowledge(stubSource{profile: knowledge.Profile{Text: "I value small diffs.", Path: "/home/u/.antidrift/knowledge.md"}})
+	r := s.Router()
+	if w := post(t, r, "/planning", ""); w.Code != http.StatusOK {
+		t.Fatalf("/planning code %d", w.Code)
+	}
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if kv := s.ctrl.State().Knowledge; kv != nil && kv.Status == "ready" {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+	js := s.stateJSON()
+	if !strings.Contains(js, `"knowledge"`) || !strings.Contains(js, `"status":"ready"`) {
+		t.Fatalf("planning payload missing knowledge object: %s", js)
+	}
+	if strings.Contains(js, "small diffs") {
+		t.Fatalf("profile text must NOT cross the wire: %s", js)
+	}
+}
+
+func TestKnowledgePathSelectionReloads(t *testing.T) {
+	s := newTestServer(t)
+	s.ctrl.SetKnowledge(stubSource{profile: knowledge.Profile{Path: "/default"}})
+	r := s.Router()
+	if w := post(t, r, "/planning", ""); w.Code != http.StatusOK {
+		t.Fatalf("/planning code %d", w.Code)
+	}
+	if w := post(t, r, "/knowledge/path", `{"path":"/custom/profile.md"}`); w.Code != http.StatusOK {
+		t.Fatalf("/knowledge/path code %d body %s", w.Code, w.Body.String())
+	}
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		if kv := s.ctrl.State().Knowledge; kv != nil && kv.Path == "/custom/profile.md" {
+			return
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+	t.Fatalf("path selection did not reload: %+v", s.ctrl.State().Knowledge)
+}