feat(computer): SSH computer selection + status + workspace default (handoff #2)

Mirrors the cwd/workspace UI for the SSH-computer feature:

- New feature library src/features/computer/:
  - logic/view-model.ts (pure): viewComputer/viewComputerStatus/viewTestResult/
    summarizeComputers/formatHost/knownHostLabel + state->badge for the 4
    ComputerStatusResponse states + SaveComputer/LoadComputerStatus/
    TestComputer/LoadComputers ports. 20 view-model tests.
  - ui/ComputerField.svelte: per-conversation selector (dropdown +
    connection-status badge + Test-connection, polling the selected alias).
  - ui/ComputerSelect.svelte: reusable Local/computers dropdown, shared with
    the workspace default-computer control.
- AppStore: computerId state + refreshComputer (at every focus site, parallel
  to refreshCwd) + setComputer (PUT /conversations/:id/computer, null=clear) +
  global computers catalog (GET /computers on boot, like models) +
  computerStatus(alias) + testComputer(alias). chat.send UNCHANGED (resolved
  server-side like cwd).
- App.svelte: ComputerField in the Model sidebar view next to CwdField; adapted
  ports wrap the store.
- workspaces: setDefaultComputer on WorkspaceHttp+WorkspaceStore
  (PUT /workspaces/:id/default-computer); default-computer selector in
  WorkspaceCard (reuses ComputerSelect); router passes store.computers through.
- Re-mirrored .dispatch/transport-contract.reference.md (Computers section +
  ChatRequest.computerId); updated .dispatch/wire.reference.md (Computer/
  ComputerEntry/defaultComputerId + the provider-retry divergence note from
  handoff #1); GLOSSARY + backend-handoff.md (handoff #2, §2e).

Transparency invariant: the computer is USER-facing only (a tool-execution
target, never part of the model prompt); the agent never sees it.

Verify: 795/795 tests green; biome clean; vite build succeeds; 0 typecheck
errors from the computer feature. (11 pre-existing svelte-check errors remain
from the open §2d provider-retry divergence — backend feature/ssh-support
still lacks TurnProviderRetryEvent; not from this feature.)

1 files changed, 42 insertions, 0 deletions

diff --git a/src/app/App.svelte b/src/app/App.svelte
index 18be3ea..78504bb 100644
--- a/src/app/App.svelte
+++ b/src/app/App.svelte
@@ -50,6 +50,16 @@
 		manifest as cwdLspManifest,
 	} from "../features/cwd-lsp";
 	import {
+		ComputerField,
+		manifest as computerManifest,
+		type ComputerSaveResult,
+		type ComputerStatusResult,
+		type LoadComputerStatus,
+		type SaveComputer,
+		type TestComputer,
+		type TestComputerResult,
+	} from "../features/computer";
+	import {
 		SystemPromptBuilder,
 		type LoadSystemPrompt as LoadSystemPromptAlias,
 		type LoadSystemPromptVariables as LoadSystemPromptVariablesAlias,
@@ -116,6 +126,7 @@
 		cacheWarmingManifest,
 		cwdLspManifest,
 		mcpManifest,
+		computerManifest,
 		smartScrollManifest,
 		settingsManifest,
 		systemPromptManifest,
@@ -311,6 +322,29 @@
 			: { ok: false, error: result.error };
 	}
 
+	// Adapt the store's computer results to the computer feature's ports.
+	async function saveComputer(computerId: string | null): Promise<ComputerSaveResult | null> {
+		const result = await store.setComputer(computerId);
+		if (result === null) return null;
+		return result.ok ? { ok: true, computerId: result.computerId } : { ok: false, error: result.error };
+	}
+
+	const loadComputerStatus: LoadComputerStatus = async (
+		alias: string,
+	): Promise<ComputerStatusResult | null> => {
+		const result = await store.computerStatus(alias);
+		if (result === null) return null;
+		return result.ok ? { ok: true, status: result.response } : { ok: false, error: result.error };
+	};
+
+	const testComputer: TestComputer = async (
+		alias: string,
+	): Promise<TestComputerResult | null> => {
+		const result = await store.testComputer(alias);
+		if (result === null) return null;
+		return result.ok ? { ok: true, response: result.response } : { ok: false, error: result.error };
+	};
+
 	async function loadMcpStatus(): Promise<McpStatusResult | null> {
 		const result = await store.mcpStatus();
 		if (result === null) return null;
@@ -493,6 +527,14 @@
 			{#key store.currentConversationId}
 				<ReasoningEffortSelector persisted={store.reasoningEffort} save={saveReasoningEffort} />
 				<CwdField cwd={store.cwd} canEdit={true} save={saveCwd} />
+				<ComputerField
+					computerId={store.computerId}
+					canEdit={true}
+					computers={store.computers}
+					save={saveComputer}
+					loadStatus={loadComputerStatus}
+					test={testComputer}
+				/>
 			{/key}
 		</div>
 	{:else if kind === "lsp"}