subagent: inherit parent context via parent= parameter

Sub-agents now clone the parent agent's conversation history into
their initial context. The tool script passes parent=$OLLIE_UNAME
automatically. Mechanically identical to session restore — uses
RestoreHistoryFromMessages on the parent's Messages().

cmd/olliesrv/internal/fs/spec.go

@@ -290,7 +290,14 @@ func buildSessionChildren(
 			virtfs.FileNode("new", 0666,
 				virtfs.Doc("Create agent. With prompt=, runs as sub-agent: blocks until done, returns reply."),
 				virtfs.Rdwr(func(ctx context.Context, data []byte) ([]byte, error) {
-					params, prompt := parseAgentNewRequest(data)
+					params, prompt, parentID := parseAgentNewRequest(data)
+
+					// Sub-agent inherits parent's context.
+					if prompt != "" && parentID != "" {
+						if parent := s.FindAgent(parentID); parent != nil {
+							params.History = agent.RestoreHistoryFromMessages(parent.Messages())
+						}
+					}
 
 					ag, err := session.CreateAgentWithParams(s.Name(), params)
 					if err != nil {

cmd/olliesrv/internal/fs/support.go

@@ -84,11 +84,11 @@ var (
 //   - Space-separated key=value (legacy format from GUI)
 //
 // A bare word (no =) is treated as the profile name (legacy positional arg).
-// Returns AgentParams and the prompt (empty if not a sub-agent request).
+// Returns AgentParams, the prompt (empty if not a sub-agent request), and the parent agent ID.
-func parseAgentNewRequest(data []byte) (session.AgentParams, string) {
+func parseAgentNewRequest(data []byte) (session.AgentParams, string, string) {
 	s := strings.TrimSpace(string(data))
 	if s == "" {
-		return session.AgentParams{Profile: "default"}, ""
+		return session.AgentParams{Profile: "default"}, "", ""
 	}
 
 	var tokens []string
@@ -99,7 +99,7 @@ func parseAgentNewRequest(data []byte) (session.AgentParams, string) {
 	}
 
 	p := session.AgentParams{Profile: "default"}
-	var prompt string
+	var prompt, parent string
 	for _, tok := range tokens {
 		tok = strings.TrimSpace(tok)
 		if tok == "" {
@@ -122,10 +122,12 @@ func parseAgentNewRequest(data []byte) (session.AgentParams, string) {
 				p.Profile = v
 			case "prompt":
 				prompt = v
+			case "parent":
+				parent = v
 			}
 		} else if p.Profile == "default" {
 			p.Profile = tok
 		}
 	}
-	return p, prompt
+	return p, prompt, parent
 }

data/tools/subagent_spawn

@@ -32,6 +32,7 @@ escaped_prompt=$(printf '%s' "$prompt_text" | sed 's/\\/\\\\/g; s/$/\\n/' | tr -
 # Build the payload.
 payload="cwd=${cwd}
 profile=${profile}
+parent=${OLLIE_UNAME}
 prompt=${escaped_prompt}"
 
 [ -n "$name" ] && payload="${payload}

doc/evolution.md

@@ -1542,6 +1542,15 @@ landed as pure wiring because:
 No new abstractions. No new processes. No new protocols. Just connecting
 existing pieces with 42 lines of glue.
 
+### Context inheritance
+
+Sub-agents inherit the parent's conversation history. When `parent=` is
+specified in the payload, the handler clones the parent agent's messages
+into the sub-agent's initial context via `RestoreHistoryFromMessages`.
+This is mechanically identical to session restore — same function, same
+data path. The sub-agent knows everything the parent knows without
+rediscovering it.
+
 ### Future work
 
 - **Shared toolsrv per host** — currently each session spawns its own toolsrv.