feat(compaction): conversation compacting + auto-compact threshold

Consume the compaction handoff ([email protected], [email protected]).
Re-pinned file: deps + re-mirrored .dispatch/*.reference.md.

- New 'Compaction' sidebar view (CompactionView.svelte):
  - 'Compact now' button → POST /conversations/:id/compact (loading indicator
    + result: 'N messages summarized, M kept')
  - Auto-compact threshold number input → GET/PUT
    /conversations/:id/compact-threshold (0 = disabled, default 350000)
  - Re-mounts per conversation via {#key}
- App store: compactNow() + compactThreshold reactive state +
  setCompactThreshold(), seeded on focus change (like reasoning-effort + cwd)
- conversation.compacted WS handler: reloads the SAME conversation's history
  (ID unchanged — old history forked to an archive, not a tab switch)
- WS adapter parses newConversationId field on ConversationCompactedMessage
- conformance guards + tests cover the new type

686 tests green.

1 files changed, 47 insertions, 2 deletions

diff --git a/src/app/App.svelte b/src/app/App.svelte
index e065759..350db49 100644
--- a/src/app/App.svelte
+++ b/src/app/App.svelte
@@ -10,11 +10,14 @@
 	} from "../features/cache-warming";
 	import {
 		ChatView,
+		CompactionView,
 		Composer,
 		manifest as chatManifest,
 		ModelSelector,
 		ReasoningEffortSelector,
+		type CompactNowResult,
 		type ReasoningEffortSaveResult,
+		type SaveCompactThresholdResult,
 	} from "../features/chat";
 	import { manifest as conversationCacheManifest } from "../features/conversation-cache";
 	import { manifest as markdownManifest } from "../features/markdown";
@@ -65,11 +68,20 @@
 		{ id: "extensions", label: "Extensions" },
 		{ id: "cache-warming", label: "Cache Warming" },
 		{ id: "tasks", label: "Tasks" },
+		{ id: "compaction", label: "Compaction" },
 		{ id: "settings", label: "Settings" },
 	] as const;
 
-	// Default sidebar layout: Model, Language Servers, Extensions, Cache Warming, Tasks, Settings.
-	const initialViews = ["model", "lsp", "extensions", "cache-warming", "tasks", "settings"] as const;
+	// Default sidebar layout: Model, Language Servers, Extensions, Cache Warming, Tasks, Compaction, Settings.
+	const initialViews = [
+		"model",
+		"lsp",
+		"extensions",
+		"cache-warming",
+		"tasks",
+		"compaction",
+		"settings",
+	] as const;
 
 	// Frontend module list for the "Loaded Modules" view, AGGREGATED from each
 	// feature's public `manifest` export so it can't drift from what's actually
@@ -211,6 +223,29 @@
 			: { ok: false, error: result.error };
 	}
 
+	// Adapt the store's compact result to the compaction view's port.
+	async function compactNow(): Promise<CompactNowResult | null> {
+		const result = await store.compactNow();
+		if (result === null) return null;
+		return result.ok
+			? {
+					ok: true,
+					messagesSummarized: result.response.messagesSummarized,
+					messagesKept: result.response.messagesKept,
+				}
+			: { ok: false, error: result.error };
+	}
+
+	async function saveCompactThreshold(
+		threshold: number,
+	): Promise<SaveCompactThresholdResult | null> {
+		const result = await store.setCompactThreshold(threshold);
+		if (result === null) return null;
+		return result.ok
+			? { ok: true, threshold: result.threshold }
+			: { ok: false, error: result.error };
+	}
+
 	// Adapt the store's chat-limit result to the settings feature's port. On a
 	// raise the active chat refills (prepends older history); preserve the
 	// reader's viewport over the prepend (the manual analogue of CSS scroll
@@ -426,6 +461,16 @@
 				<p class="text-xs opacity-60">No tasks yet.</p>
 			{/if}
 		{/key}
+	{:else if kind === "compaction"}
+		<!-- Re-mount per conversation so the threshold + feedback can't bleed across tabs. -->
+		{#key store.currentConversationId}
+			<CompactionView
+				threshold={store.compactThreshold}
+				canCompact={store.activeConversationId !== null}
+				{compactNow}
+				saveThreshold={saveCompactThreshold}
+			/>
+		{/key}
 	{:else if kind === "settings"}
 		<!-- FE-local settings. Not conversation-scoped (no {#key}: the chat limit is
 		     global), so the field stays mounted across tab switches. -->