diff --git a/tools/ui/tests/unit/agentic-sections.test.ts b/tools/ui/tests/unit/agentic-sections.test.ts
index 4096a17107..fdb3b22178 100644
--- a/tools/ui/tests/unit/agentic-sections.test.ts
+++ b/tools/ui/tests/unit/agentic-sections.test.ts
@@ -290,3 +290,114 @@ describe('hasAgenticContent', () => {
 		expect(hasAgenticContent(msg)).toBe(false);
 	});
 });
+
+// The turn-section cache: completed turns are immutable, so repeated
+// derivations return the same section objects - which is what keeps tool
+// block props stable while another turn streams. Every field the cache
+// compares must invalidate it; a miss here renders stale content.
+
+describe('completed turn section reuse', () => {
+	const toolCallsJson = JSON.stringify([
+		{ function: { arguments: '{"path":"/a"}', name: 'test' }, id: 'call_1', type: 'function' }
+	]);
+
+	function makeSession() {
+		return {
+			anchor: makeAssistant({
+				content: 'answer',
+				reasoningContent: 'thinking',
+				toolCalls: toolCallsJson
+			}),
+			tools: [makeToolMsg({ content: 'tool result', extra: [{ type: 'file' } as never] })]
+		};
+	}
+
+	it('returns the same section objects for unchanged inputs', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], false);
+		const second = deriveAgenticSections(anchor, tools, [], false);
+
+		expect(second[0]).toBe(first[0]);
+		expect(second[1]).toBe(first[1]);
+	});
+
+	it('recomputes when the assistant content changes', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], false);
+
+		anchor.content = 'edited';
+		const second = deriveAgenticSections(anchor, tools, [], false);
+
+		expect(second).not.toBe(first);
+		expect(second.some((s) => s.type === AgenticSectionType.TEXT && s.content === 'edited')).toBe(
+			true
+		);
+	});
+
+	it('recomputes when reasoning content changes', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], false);
+
+		anchor.reasoningContent = 'new thinking';
+		const second = deriveAgenticSections(anchor, tools, [], false);
+
+		expect(second).not.toBe(first);
+	});
+
+	it('recomputes when toolCalls change', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], false);
+
+		anchor.toolCalls = '[]';
+		const second = deriveAgenticSections(anchor, tools, [], false);
+
+		expect(second).not.toBe(first);
+	});
+
+	it('recomputes when a tool result or its extras change', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], false);
+
+		tools[0].content = 'new tool result';
+		expect(deriveAgenticSections(anchor, tools, [], false)).not.toBe(first);
+
+		const firstAfterContent = deriveAgenticSections(anchor, tools, [], false);
+
+		tools[0].extra = [{ type: 'image' } as never];
+		expect(deriveAgenticSections(anchor, tools, [], false)).not.toBe(firstAfterContent);
+	});
+
+	it('never reuses the streaming turn', () => {
+		const { anchor, tools } = makeSession();
+		const first = deriveAgenticSections(anchor, tools, [], true);
+		const second = deriveAgenticSections(anchor, tools, [], true);
+
+		expect(second).not.toBe(first);
+	});
+
+	it('keeps completed turns stable while the last turn streams', () => {
+		const anchor = makeAssistant({
+			content: 'turn one',
+			id: 'ast-1',
+			toolCalls: JSON.stringify([
+				{ function: { arguments: '{}', name: 'test' }, id: 'call_1', type: 'function' }
+			])
+		});
+		const continuation = makeAssistant({ content: 'turn two', id: 'ast-2' });
+		const tools = [
+			makeToolMsg({ content: 'r1', id: 'tool-1', toolCallId: 'call_1' }),
+			continuation,
+			makeToolMsg({ content: 'r2', id: 'tool-2', toolCallId: 'call_2' })
+		];
+		const first = deriveAgenticSections(anchor, tools, [], true);
+		const second = deriveAgenticSections(anchor, tools, [], true);
+
+		// turn one is complete: identical section objects across derivations
+		expect(second.slice(0, 2)).toEqual(first.slice(0, 2));
+		expect(second[0]).toBe(first[0]);
+		expect(second[1]).toBe(first[1]);
+
+		// the streaming last turn recomputed: fresh section objects
+		expect(second[second.length - 1]).not.toBe(first[first.length - 1]);
+	});
+});
diff --git a/tools/ui/tests/unit/branching.test.ts b/tools/ui/tests/unit/branching.test.ts
new file mode 100644
index 0000000000..8a752ae2f1
--- /dev/null
+++ b/tools/ui/tests/unit/branching.test.ts
@@ -0,0 +1,95 @@
+// Sibling-info correctness for buildSiblingInfoMap, including the memoized
+// leaf resolution. A wrong leaf id here breaks branch navigation, so the
+// deep-chain and multi-branch cases below pin the resolution down.
+
+import { MessageRole, MessageType } from '$lib/enums';
+import type { DatabaseMessage } from '$lib/types/database';
+import { buildSiblingInfoMap, findLeafNode } from '$lib/utils/branching';
+import { describe, expect, it } from 'vitest';
+
+function msg(id: string, parent: string | null, children: string[] = []): DatabaseMessage {
+	return {
+		children,
+		content: '',
+		convId: 'c1',
+		id,
+		parent,
+		role: MessageRole.USER,
+		timestamp: 0,
+		type: MessageType.TEXT
+	} as DatabaseMessage;
+}
+
+/** root -> m1 -> ... -> m depth, each node with a single child. */
+function linearChain(depth: number): DatabaseMessage[] {
+	const messages = [msg('m0', null, ['m1'])];
+
+	for (let i = 1; i <= depth; i++) {
+		messages.push(msg(`m${i}`, `m${i - 1}`, i < depth ? [`m${i + 1}`] : []));
+	}
+
+	return messages;
+}
+
+describe('buildSiblingInfoMap', () => {
+	it('resolves the deepest leaf for every node of a long single chain', () => {
+		const messages = linearChain(50);
+		const map = buildSiblingInfoMap(messages);
+		const leafId = messages[messages.length - 1].id;
+
+		// every non-root message of the chain is an only child, and its
+		// navigation target is the chain's deepest leaf
+		for (const m of messages.slice(1)) {
+			const info = map.get(m.id);
+
+			expect(info?.totalSiblings).toBe(1);
+			expect(info?.siblingIds).toEqual([leafId]);
+		}
+	});
+
+	it('reports sibling position and leaf targets on a branched tree', () => {
+		// m0 -> m1, m4 ; m1 -> m2 ; m2 -> m3, m6 ; m4 -> m5
+		const root = msg('m0', null, ['m1', 'm4']);
+		const m1 = msg('m1', 'm0', ['m2']);
+		const m2 = msg('m2', 'm1', ['m3', 'm6']);
+		const m3 = msg('m3', 'm2');
+		const m4 = msg('m4', 'm0', ['m5']);
+		const m5 = msg('m5', 'm4');
+		const m6 = msg('m6', 'm2');
+		const map = buildSiblingInfoMap([root, m1, m2, m3, m4, m5, m6]);
+
+		// m1 and m4 share the root as parent; their nav targets are the
+		// leaves of their subtrees ( m6 for the first branch, m5 for the second )
+		expect(map.get(m1.id)).toMatchObject({
+			currentIndex: 0,
+			siblingIds: [m6.id, m5.id],
+			totalSiblings: 2
+		});
+		expect(map.get(m4.id)).toMatchObject({
+			currentIndex: 1,
+			siblingIds: [m6.id, m5.id],
+			totalSiblings: 2
+		});
+
+		// m3 and m6 are siblings under m2; both are leaves
+		expect(map.get(m3.id)?.siblingIds).toEqual([m3.id, m6.id]);
+		expect(map.get(m6.id)?.currentIndex).toBe(1);
+
+		// the root has no parent and reports itself
+		expect(map.get(root.id)).toMatchObject({
+			currentIndex: 0,
+			siblingIds: [root.id],
+			totalSiblings: 1
+		});
+	});
+
+	it('agrees with findLeafNode for arbitrary nodes', () => {
+		const messages = linearChain(20);
+		const leafId = messages[messages.length - 1].id;
+
+		// every node of the chain resolves to the deepest leaf
+		for (const m of messages) {
+			expect(findLeafNode(messages, m.id), `leaf of ${m.id}`).toBe(leafId);
+		}
+	});
+});
diff --git a/tools/ui/tests/unit/conversations-store.test.ts b/tools/ui/tests/unit/conversations-store.test.ts
new file mode 100644
index 0000000000..e06546597b
--- /dev/null
+++ b/tools/ui/tests/unit/conversations-store.test.ts
@@ -0,0 +1,90 @@
+// Field updates to the active conversation must keep the object identity
+// stable: effects that track the identity ( the chat screen's sibling-info
+// refresh ) refire on every identity change, which used to trigger a full
+// message refetch on every send and tool result.
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+vi.mock('$lib/services/database.service', () => ({
+	DatabaseService: {
+		getConversation: vi.fn(),
+		getConversationMessages: vi.fn(),
+		updateConversation: vi.fn(),
+		updateCurrentNode: vi.fn()
+	}
+}));
+
+import { DatabaseService } from '$lib/services/database.service';
+import { conversationsStore } from '$lib/stores/conversations/index.svelte';
+import type { DatabaseConversation, DatabaseMessage } from '$lib/types/database';
+
+const getConversationMock = vi.mocked(DatabaseService.getConversation);
+const getMessagesMock = vi.mocked(DatabaseService.getConversationMessages);
+const updateCurrentNodeMock = vi.mocked(DatabaseService.updateCurrentNode);
+
+function makeConversation(overrides: Partial<DatabaseConversation> = {}): DatabaseConversation {
+	return {
+		currNode: 'node-1',
+		id: 'conv-1',
+		lastModified: 1000,
+		name: 'conversation',
+		...overrides
+	};
+}
+
+async function loadActive(conversation: DatabaseConversation, messages: DatabaseMessage[]) {
+	getConversationMock.mockResolvedValue(conversation);
+	getMessagesMock.mockResolvedValue(messages);
+
+	expect(await conversationsStore.loadConversation(conversation.id)).toBe(true);
+}
+
+beforeEach(() => {
+	getConversationMock.mockReset();
+	getMessagesMock.mockReset();
+	updateCurrentNodeMock.mockReset();
+	updateCurrentNodeMock.mockResolvedValue(undefined);
+	vi.mocked(DatabaseService.updateConversation).mockReset();
+	vi.mocked(DatabaseService.updateConversation).mockResolvedValue(undefined);
+});
+
+describe('active conversation identity', () => {
+	it('hands the load read off exactly once', async () => {
+		await loadActive(makeConversation(), []);
+
+		expect(conversationsStore.consumeLastLoadedMessages('conv-1')).toEqual([]);
+		// a second consume is a miss: branch actions must fall back to a refetch
+		expect(conversationsStore.consumeLastLoadedMessages('conv-1')).toBeNull();
+	});
+
+	it('writes currNode in place on updateCurrentNode', async () => {
+		await loadActive(makeConversation(), []);
+		const before = conversationsStore.activeConversation;
+
+		await conversationsStore.updateCurrentNode('node-2');
+
+		expect(conversationsStore.activeConversation).toBe(before);
+		expect(conversationsStore.activeConversation?.currNode).toBe('node-2');
+	});
+
+	it('writes renamed and pinned fields in place on applyConversationUpdate', async () => {
+		await loadActive(makeConversation(), []);
+		const before = conversationsStore.activeConversation;
+
+		conversationsStore.applyConversationUpdate('conv-1', { name: 'renamed', pinned: true });
+
+		expect(conversationsStore.activeConversation).toBe(before);
+		expect(conversationsStore.activeConversation?.name).toBe('renamed');
+		expect(conversationsStore.activeConversation?.pinned).toBe(true);
+	});
+
+	it('writes lastModified in place on updateConversationTimestamp', async () => {
+		await loadActive(makeConversation(), []);
+		const before = conversationsStore.activeConversation;
+
+		conversationsStore.updateConversationTimestamp('conv-1');
+
+		expect(conversationsStore.activeConversation).toBe(before);
+		expect(conversationsStore.activeConversation?.lastModified).toBeGreaterThan(1000);
+	});
+});
diff --git a/tools/ui/tests/unit/parse-exec-shell-status.test.ts b/tools/ui/tests/unit/parse-exec-shell-status.test.ts
index ed499d078e..7e22bf9eeb 100644
--- a/tools/ui/tests/unit/parse-exec-shell-status.test.ts
+++ b/tools/ui/tests/unit/parse-exec-shell-status.test.ts
@@ -71,3 +71,21 @@ describe('isExitCodeSummaryLine', () => {
 		expect(isExitCodeSummaryLine('[exit code: 7]', undefined)).toBe(false);
 	});
 });
+
+describe('parseExecShellCommandExitStatus tail scan', () => {
+	it('finds the marker at the end of a blob larger than the tail window', () => {
+		// the parser matches only the last ~128 chars; a marker past that
+		// window must still parse, and an earlier fake must not match
+		const blob = `${'the shell prints [exit code: 1] mid-stream\n'.repeat(2000)}[exit code: 0]`;
+		const status = parseExecShellCommandExitStatus(blob);
+
+		expect(status?.code).toBe(0);
+		expect(status?.timedOut).toBe(false);
+	});
+
+	it('keeps rejecting markers that are not at the absolute end', () => {
+		const blob = `${'stdout\n'.repeat(2000)}[exit code: 0]\nsome trailing log line`;
+
+		expect(parseExecShellCommandExitStatus(blob)).toBeUndefined();
+	});
+});
diff --git a/tools/ui/tests/unit/search-results.test.ts b/tools/ui/tests/unit/search-results.test.ts
index c168dec258..561ab935a8 100644
--- a/tools/ui/tests/unit/search-results.test.ts
+++ b/tools/ui/tests/unit/search-results.test.ts
@@ -2,7 +2,8 @@ import {
 	extractSearchQuery,
 	extractSearchResults,
 	faviconForUrl,
-	isWebSearchToolName
+	isWebSearchToolName,
+	looksLikeSearchResult
 } from '$lib/utils/search-results';
 import { describe, expect, it } from 'vitest';
 
@@ -119,3 +120,27 @@ describe('isWebSearchToolName', () => {
 		expect(isWebSearchToolName('exec_shell_command')).toBe(false);
 	});
 });
+
+describe('extractSearchResults prefilter', () => {
+	it('returns the shared empty array for blobs without the wire format', () => {
+		// exec/file tool results never carry Title:/URL: field lines; the
+		// cheap prefilter must skip the line-split parse for them
+		const stdout = `${'make[1]: entering directory\n'.repeat(5000)}`;
+
+		expect(extractSearchResults(stdout)).toEqual([]);
+	});
+
+	it('returns an empty result when only one required field is present', () => {
+		expect(extractSearchResults('URL: https://example.com')).toEqual([]);
+		expect(extractSearchResults('Title: only a title')).toEqual([]);
+	});
+});
+
+describe('looksLikeSearchResult', () => {
+	it('requires both Title and URL field markers', () => {
+		expect(looksLikeSearchResult('Title: a\nURL: https://b')).toBe(true);
+		expect(looksLikeSearchResult('URL: https://b')).toBe(false);
+		expect(looksLikeSearchResult('plain stdout')).toBe(false);
+		expect(looksLikeSearchResult(undefined)).toBe(false);
+	});
+});
diff --git a/tools/ui/tests/unit/tool-call-meta.test.ts b/tools/ui/tests/unit/tool-call-meta.test.ts
index bb28e3830c..f94d2279fe 100644
--- a/tools/ui/tests/unit/tool-call-meta.test.ts
+++ b/tools/ui/tests/unit/tool-call-meta.test.ts
@@ -28,3 +28,15 @@ describe('tryParseToolResultObject', () => {
 		expect(tryParseToolResultObject('{bad')).toBeNull();
 	});
 });
+
+describe('tryParseToolResultObject gating', () => {
+	it('parses JSON objects that start after leading whitespace', () => {
+		expect(tryParseToolResultObject('\n  {"result":"ok"}')).toEqual({ result: 'ok' });
+	});
+
+	it('skips the parse for large plain-text results', () => {
+		// most tool results are file contents or stdout; the gate avoids a
+		// doomed JSON.parse over the whole blob
+		expect(tryParseToolResultObject(`${'stdout line\n'.repeat(2000)}`)).toBeNull();
+	});
+});