fix(coding-agent): preserve branch summary source leaf

Record the pre-navigation leaf in branch summary fromId instead of the destination node.

packages/coding-agent/CHANGELOG.md

@@ -19,6 +19,7 @@
 - Fixed llama.cpp login guidance to direct users to `/llama` before `/model` when no local models are loaded ([#8203](https://github.com/earendil-works/pi/issues/8203)).
 - Fixed hung pi.dev model catalog requests consuming the entire refresh deadline without retrying ([#8198](https://github.com/earendil-works/pi/issues/8198)).
 - Fixed inherited Xiaomi model catalogs listing shut-down MiMo V2 models in `/model` and `--list-models` ([#8187](https://github.com/earendil-works/pi/issues/8187)).
+- Fixed branch summary entries recording the navigation destination in `fromId` instead of the pre-navigation source leaf.
 
 ## [0.84.2] - 2026-08-14
 

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

@@ -1388,13 +1388,14 @@ export class SessionManager {
 		if (branchFromId !== null && !this.byId.has(branchFromId)) {
 			throw new Error(`Entry ${branchFromId} not found`);
 		}
+		const fromId = this.leafId ?? "root";
 		this.leafId = branchFromId;
 		const entry: BranchSummaryEntry = {
 			type: "branch_summary",
 			id: generateId(this.byId),
 			parentId: branchFromId,
 			timestamp: new Date().toISOString(),
-			fromId: branchFromId ?? "root",
+			fromId,
 			summary,
 			details,
 			usage,

packages/coding-agent/test/branch-summary-extensions.test.ts

@@ -38,12 +38,14 @@ describe("Branch summary extensions", () => {
 		const targetId = harness.sessionManager.appendMessage(userMsg("first branch"));
 		harness.sessionManager.appendMessage(assistantMsg("first reply"));
 		harness.sessionManager.appendMessage(userMsg("abandoned branch work"));
-		harness.sessionManager.appendMessage(assistantMsg("abandoned reply"));
+		const sourceId = harness.sessionManager.appendMessage(assistantMsg("abandoned reply"));
 
 		const result = await harness.session.navigateTree(targetId, { summarize: true });
 		const summaryEntry = result.summaryEntry;
 
 		expect(summaryEntry?.type).toBe("branch_summary");
+		expect(summaryEntry?.parentId).toBeNull();
+		expect(summaryEntry?.fromId).toBe(sourceId);
 		expect(summaryEntry?.fromHook).toBe(true);
 		expect(summaryEntry?.summary).toBe("Summary provided by extension");
 		expect(summaryEntry?.usage).toEqual(usage);

packages/coding-agent/test/session-manager/tree-traversal.test.ts

@@ -321,12 +321,12 @@ describe("SessionManager append and tree traversal", () => {
 	});
 
 	describe("branchWithSummary", () => {
-		it("inserts branch summary and advances leaf", () => {
+		it("inserts branch summary with the source and destination and advances leaf", () => {
 			const session = SessionManager.inMemory();
 
 			const id1 = session.appendMessage(userMsg("1"));
 			const _id2 = session.appendMessage(assistantMsg("2"));
-			const _id3 = session.appendMessage(userMsg("3"));
+			const id3 = session.appendMessage(userMsg("3"));
 
 			const usage = {
 				input: 10,
@@ -345,6 +345,7 @@ describe("SessionManager append and tree traversal", () => {
 			expect(summaryEntry).toBeDefined();
 			expect(summaryEntry?.parentId).toBe(id1);
 			if (summaryEntry?.type === "branch_summary") {
+				expect(summaryEntry.fromId).toBe(id3);
 				expect(summaryEntry.summary).toBe("Summary of abandoned work");
 				expect(summaryEntry.usage).toEqual(usage);
 			}