fix(coding-agent): dedupe session tree edges

packages/coding-agent/CHANGELOG.md

@@ -6,6 +6,8 @@
 
 ### Fixed
 
+- Session tree construction no longer freezes on sessions with duplicate entry IDs; `getTree()` builds one edge per unique node instead of re-linking the same node for every persisted row ([#1247](https://github.com/code-yeongyu/senpi/issues/1247)).
+
 - Multi-session RPC hosts launched with `SENPI_RPC_CLIENT_CAPABILITIES` (for example `extension_events`) now apply those capabilities to connection-owned session bindings when the client never sends `set_client_info`. Previously the launch capabilities were advertised through `get_protocol_info` but dropped at binding creation, so undeclared clients received no `extension_event` frames (breaking downstream task/DAG/monitor liveness in omo-desktop-app). An explicit `set_client_info` declaration, including an empty capability list, still overrides the launch default.
 
 - RPC `abort` acknowledgements are now sent immediately after the abort signal is dispatched instead of waiting for full session quiescence, preventing desktop stop requests from hitting their 10-second bounded-ack timeout under host load.

packages/coding-agent/src/core/changes.md

@@ -1,5 +1,23 @@
 # changes
 
+## 2026-09-01 - Bound session tree construction with duplicate entry IDs
+
+### What changed
+
+- `packages/coding-agent/src/core/session-manager.ts`: `SessionManager.getTree()` now links each unique entry ID once, while preserving the existing final-entry-wins index semantics for repeated persisted rows.
+
+### Why
+
+- Duplicate entry IDs caused the same `SessionTreeNode` object to be appended repeatedly to a parent's children. Repeated duplicate edges along a branch multiplied the later traversal work and could freeze the interactive session tree before it rendered.
+
+### Why an extension could not handle it
+
+- Persisted session indexing and tree construction are core `SessionManager` responsibilities below the extension API. An extension cannot replace the synchronous tree returned to interactive, RPC, and other consumers.
+
+### Expected merge conflict zones
+
+- LOW: the edge-construction loop in `packages/coding-agent/src/core/session-manager.ts`.
+
 ## 2026-08-31 - Session activity contract for host occupancy decisions
 
 ### What changed

packages/coding-agent/src/core/session-manager.ts

@@ -1568,9 +1568,10 @@ export class SessionManager {
 			nodeMap.set(entry.id, { entry, children: [], label, labelTimestamp });
 		}
 
-		// Build tree
-		for (const entry of entries) {
-			const node = nodeMap.get(entry.id)!;
+		// Build one edge per unique ID. Persisted sessions can contain repeated rows,
+		// and nodeMap intentionally keeps the final entry for each ID.
+		for (const node of nodeMap.values()) {
+			const { entry } = node;
 			if (entry.parentId === null || entry.parentId === entry.id) {
 				roots.push(node);
 			} else {

packages/coding-agent/test/suite/regressions/issue-1247-session-tree-duplicate-entry-ids.test.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from "vitest";
+import { type CustomEntry, SessionManager } from "../../../src/core/session-manager.ts";
+
+function customEntry(id: string, parentId: string | null, revision: number): CustomEntry {
+	return {
+		type: "custom",
+		customType: "duplicate-id-regression",
+		data: { revision },
+		id,
+		parentId,
+		timestamp: `2026-09-01T00:00:0${revision}.000Z`,
+	};
+}
+
+describe("issue #1247 duplicate session entry IDs", () => {
+	it("builds one tree node per entry ID when persisted rows repeat", () => {
+		// Given: a persisted-style chain where the same child ID appears twice.
+		const session = SessionManager.inMemory();
+		session.appendEntry(customEntry("root", null, 0));
+		session.appendEntry(customEntry("child", "root", 1));
+		session.appendEntry(customEntry("child", "root", 2));
+		session.appendEntry(customEntry("grandchild", "child", 3));
+
+		// When: the session tree is constructed.
+		const tree = session.getTree();
+
+		// Then: the last row for the duplicate ID wins without adding duplicate edges.
+		expect(tree).toHaveLength(1);
+		expect(tree[0]?.entry.id).toBe("root");
+		expect(tree[0]?.children.map((node) => node.entry.id)).toEqual(["child"]);
+		expect(tree[0]?.children[0]?.entry).toMatchObject({
+			id: "child",
+			data: { revision: 2 },
+		});
+		expect(tree[0]?.children[0]?.children.map((node) => node.entry.id)).toEqual(["grandchild"]);
+	});
+});