feat(tasks): phase 3 — close the knowledge loop (complete_task + retrieval)

Adds the compounding knowledge loop the task model is built around:

- complete_task(outcome, summary): a nomos-LOCAL, session-scoped tool (the
  shared MCP server has no session id). Introduces the local-tool mechanism —
  buildTools appends task tools, the agent loop routes them to handleTaskTool
  instead of the MCP client. Sets the task's terminal status/outcome/summary,
  mirrors it onto the task entity, and emits task.status.
- Knowledge → task linkage: after a successful upsert_knowledge in a task,
  nomos links the note to the task entity (documents) and emits
  knowledge.recorded, so the task's outcome view shows what it learned. The
  note's about-link to the involved entity (written by upsert_knowledge) is the
  retrieval path future tasks use.
- SOUL: every chat is a task loop — retrieve prior knowledge FIRST
  (get_entity_knowledge on the target), plan, execute, record learnings, then
  complete_task. Scales down for trivial read-only tasks.
- deleteSession now cleans up the task entity, its relationships, and its
  task-scoped events (was orphaning them); the knowledge doc itself and its
  about-links survive, as knowledge should outlive the task.

Verified end-to-end: a task recorded a note and completed; task.status +
knowledge.recorded hit the SSE stream; status=done/outcome=success persisted;
the note linked to both lxc:caddy (retrieval) and the task; a future
get_entity_knowledge(lxc:caddy) surfaces it; delete cleaned edges+events (0/0/0)
while the knowledge survived.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/nomos/tasks.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+// Task tools are nomos-LOCAL, not MCP tools. They are session-scoped, and the
+// shared MCP server (api:8090/mcp) has no session id — so these are handled
+// in-process by nomos, which knows the session/task and holds the store.
+// buildTools appends these to the model's tool list; the agent loop routes a
+// call whose name isTaskTool to handleTaskTool instead of the MCP client.
+//
+// Phase 3 ships complete_task; set_goal / propose_plan / update_plan_step /
+// ask_operator land in later phases through the same mechanism.
+
+func taskToolDefs() []toolDef {
+	return []toolDef{
+		{
+			Name: "complete_task",
+			Description: "Mark the current task finished. Call this once the goal is " +
+				"verified done — or when you've genuinely failed or only partially " +
+				"succeeded. Sets the task's outcome and a one-line summary shown on the " +
+				"task board. Record what you learned with upsert_knowledge BEFORE " +
+				"completing, so future tasks on the same entities benefit.",
+			InputSchema: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"outcome": map[string]any{
+						"type":        "string",
+						"enum":        []string{"success", "failure", "partial"},
+						"description": "Did the task achieve its goal?",
+					},
+					"summary": map[string]any{
+						"type":        "string",
+						"description": "One line describing the result (shown on the task card).",
+					},
+				},
+				"required": []string{"outcome", "summary"},
+			},
+		},
+	}
+}
+
+func isTaskTool(name string) bool {
+	switch name {
+	case "complete_task":
+		return true
+	default:
+		return false
+	}
+}
+
+// handleTaskTool executes a nomos-local task tool. Returns (result, true) if it
+// handled the call, or (nil, false) if name is not a local task tool (so the
+// caller forwards it to the MCP client).
+func (a *agent) handleTaskTool(ctx context.Context, sessionID, name string, args map[string]any) (any, bool) {
+	switch name {
+	case "complete_task":
+		outcome, _ := args["outcome"].(string)
+		summary, _ := args["summary"].(string)
+		if outcome == "" {
+			outcome = "success"
+		}
+		if err := a.store.completeTask(ctx, sessionID, outcome, summary); err != nil {
+			return fmt.Sprintf("error completing task: %v", err), true
+		}
+		return fmt.Sprintf("Task marked %s: %s", outcome, summary), true
+	default:
+		return nil, false
+	}
+}