feat: wire Infisical secret store into API server and MCP tools

- Wire secretsManager in NewHandler() — instantiate InfisicalBackend
  when OIKOS_INFISICAL_SITE_URL is set (previously always nil)
- Add get_secret, list_secrets, set_secret MCP tools with nil-backend
  graceful degradation
- Add oikos secret get|set|list CLI subcommands for Infisical
- Fix Set() bug: create-before-update so new keys are created;
  add Type: "shared" to Update so it finds the right secret;
  disable SDK cache so Get returns fresh data after Set
- Clean enrollment response: remove fake infisical_client_id/
  infisical_client_secret stubs, store age key in Infisical for real

internal/mcp/tools.go

@@ -29,7 +29,7 @@ type toolReg struct {
 // allTools returns every MCP tool registration. Tool definitions, schemas,
 // descriptions, and handler bodies are kept verbatim from the former inline
 // newServer registrations.
-func allTools(pool *db.Pool, agentID uuid.UUID) []toolReg {
+func allTools(pool *db.Pool, agentID uuid.UUID, sec secretBackend) []toolReg {
 	return []toolReg{
 		{tool: &mcp.Tool{Name: "ping", Description: "Lightweight connectivity check. Returns server identity, no DB hit.",
 			InputSchema: objSchema(),
@@ -1629,6 +1629,81 @@ func allTools(pool *db.Pool, agentID uuid.UUID) []toolReg {
 			ORDER BY e.slug
 			LIMIT $3`, key, val, limit), nil
 		}},
+
+		// ── Stage 5: Secret store (Infisical) ────────────────────────
+		{tool: &mcp.Tool{Name: "get_secret", Description: "Retrieve a secret value from the Infisical vault. Returns the secret value. Use for service credentials, tokens, and keys needed to operate the homelab.",
+			InputSchema: objSchema(
+				prop{"key", "string", "Secret key to retrieve (e.g. 'matrix-token', 'clients/host:hubris/age-key')"},
+				prop{"path", "string", "Secret path prefix (default '/')"},
+				prop{"environment", "string", "Environment slug (default 'dev')"}),
+		}, handler: func(ctx context.Context, req *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+			if sec == nil {
+				return textResult("error: no secrets backend configured (set OIKOS_INFISICAL_SITE_URL)"), nil
+			}
+			args := argsMap(req)
+			key, _ := args["key"].(string)
+			if key == "" {
+				return textResult("error: key is required"), nil
+			}
+			val, err := sec.Get(ctx, key)
+			if err != nil {
+				return textResult(fmt.Sprintf("error: %v", err)), nil
+			}
+			return textResult(val), nil
+		}},
+
+		{tool: &mcp.Tool{Name: "list_secrets", Description: "List secret keys in the Infisical vault. Returns key names only (no values). Filter by path prefix to scope to a client or shared path.",
+			InputSchema: objSchema(
+				prop{"path_prefix", "string", "Filter to keys matching this prefix (e.g. 'clients/', 'shared/', 'config/')"}),
+		}, handler: func(ctx context.Context, req *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+			if sec == nil {
+				return textResult("error: no secrets backend configured (set OIKOS_INFISICAL_SITE_URL)"), nil
+			}
+			args := argsMap(req)
+			prefix, _ := args["path_prefix"].(string)
+
+			keys, err := sec.List(ctx)
+			if err != nil {
+				return textResult(fmt.Sprintf("error: %v", err)), nil
+			}
+			if prefix != "" {
+				filtered := keys[:0]
+				for _, k := range keys {
+					if strings.HasPrefix(k, prefix) {
+						filtered = append(filtered, k)
+					}
+				}
+				keys = filtered
+			}
+			data, _ := json.MarshalIndent(keys, "", "  ")
+			return textResult(string(data)), nil
+		}},
+
+		{tool: &mcp.Tool{Name: "set_secret", Description: "Store or update a secret in the Infisical vault. Use when discovering new credentials that need to be persisted. Requires operator approval (config_mutation).",
+			InputSchema: objSchema(
+				prop{"key", "string", "Secret key to store"},
+				prop{"value", "string", "Secret value to store"},
+				prop{"path", "string", "Secret path prefix (default '/')"},
+				prop{"environment", "string", "Environment slug (default 'dev')"}),
+		}, handler: func(ctx context.Context, req *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+			if sec == nil {
+				return textResult("error: no secrets backend configured (set OIKOS_INFISICAL_SITE_URL)"), nil
+			}
+			args := argsMap(req)
+			key, _ := args["key"].(string)
+			value, _ := args["value"].(string)
+			if key == "" {
+				return textResult("error: key is required"), nil
+			}
+			if value == "" {
+				return textResult("error: value is required"), nil
+			}
+			if err := sec.Set(ctx, key, value); err != nil {
+				return textResult(fmt.Sprintf("error: %v", err)), nil
+			}
+			return textResult(fmt.Sprintf("secret %s stored", key)), nil
+		}},
+
 	}
 }