feat(parallel-agents-ui): scaffold side-bar subagent view

docs/zeus-parallel-agents-ui.md

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+# Parallel agents UI
+
+Multiple Zeus subagents run concurrently. Each one needs a visible, cancellable, observable surface — but **never as the editor's primary view**.
+
+This is the deliberate counter-positioning vs Cursor 3 / Antigravity 2.0 / Windsurf Cascade, all of which made the agent manager the home screen. The market signal (Pragmatic Engineer Feb 2026: Claude Code "most loved" 46%, more than 2× Cursor) says many senior developers prefer agents as a tool, not as their workflow's center.
+
+## Where the UI lives
+
+An **auxiliary bar view** (the right-side container in VS Code's workbench — formally "auxiliary bar"; the "side bar" is the left-side container by VS Code's own naming). Not the activity bar's first slot, not the editor center. Closeable. Reopen via command palette.
+
+```text
+┌──┬───────────────────────────┬─ Parallel agents view ──────────┐
+│  │                           │  ▶ docs-writer    streaming…    │
+│A │   Editor (primary)        │     tool: read_file             │
+│c │   user code, just like    │  ▶ test-writer    waiting on    │
+│t │   VS Code                 │     tool approval               │
+│iv│                           │  ▼ security-reviewer  done ·    │
+│it│                           │      3 findings                 │
+│y │                           │      findings.md modified       │
+│  │                           │                                 │
+├──┴───────────────────────────┴─────────────────────────────────┤
+│ Status bar  ⚡ 2 agents running · $0.41 today · cache: 92% hit │
+└────────────────────────────────────────────────────────────────┘
+   ↑ status item is always visible; clicking it focuses the
+     auxiliary-bar view (right by default, draggable to left).
+     The status bar sits at the bottom — below both the editor
+     and the auxiliary bar — per VS Code's workbench layout.
+```
+
+## Behavior
+
+- New agent: `Ctrl+K Ctrl+N` (chord) opens a quick-pick of skills from `.zeus/skills/`, runs the chosen one. The earlier draft used `Ctrl+Shift+A`, but that clashes with VS Code's `toggleSearchEditorContextLines` in the Search Editor; using a chord keeps the new shortcut out of every default scope
+- Each agent: own subtree in the view with timeline (tool calls, text deltas), final summary, cancel button, "open in chat" button
+- Done agents move to "Recent" collapsed group; never auto-dismissed
+- A finished agent's file edits are surfaced as a diff PR-style review, not auto-applied
+- Notifications: agent completion → optional status bar pulse, no modal
+
+## What this UI does **not** do
+
+- It is **not** the editor home page
+- It does not auto-open on startup unless the user pinned it
+- It does not show a "create a project plan" or "decompose this PRD" prompt
+- It does not encourage running 10 agents at once just because you can
+
+## File contracts
+
+- Source of truth for runnable skills: `.zeus/skills/*.md` (loaded by `feat/agent-sdk`)
+- Source of truth for running agents: `IAgentRuntime` events (from `feat/agent-sdk`)
+- Cost / cache state: subscribed to from `feat/prompt-cache-hud` shared store
+
+## Acceptance criteria (real impl)
+
+- [ ] Quick-pick of skills picks one and starts it
+- [ ] Auxiliary bar shows live tool-call timeline per agent
+- [ ] Cancel works mid-stream
+- [ ] Done agents persist in the view for the session
+- [ ] No auto-open behavior on startup
+- [ ] File edits are shown as diff, never applied without user "Apply"
+- [ ] Keyboard: `Ctrl+K Ctrl+N` new agent, `Ctrl+K Ctrl+A` focus list — both chords, to avoid VS Code defaults (`Ctrl+Shift+A` is `toggleSearchEditorContextLines`; `Ctrl+Shift+L` is `editor.action.selectHighlights`)
+
+## Status
+
+Slot reserved at `src/vs/workbench/contrib/parallelAgents/`.

src/vs/workbench/contrib/parallelAgents/README.md

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+# `parallelAgents` contribution
+
+Slot for the auxiliary-bar view that surfaces running and completed subagents. Design: [`docs/zeus-parallel-agents-ui.md`](../../../../../docs/zeus-parallel-agents-ui.md).
+
+The view is deliberately **not** the editor's home surface — Zeus's counter-positioning vs Cursor 3 / Antigravity 2.0 / Windsurf Cascade.
+
+## Canonical IDs
+
+The view container, view, and command identifiers are exported from [`common/parallelAgents.ts`](./common/parallelAgents.ts):
+
+- `PARALLEL_AGENTS_VIEW_CONTAINER_ID = 'zeus.parallelAgents'`
+- `PARALLEL_AGENTS_VIEW_ID = 'zeus.parallelAgents.list'`
+- `PARALLEL_AGENTS_COMMAND_NEW = 'zeus.parallelAgents.new'`
+- `PARALLEL_AGENTS_COMMAND_FOCUS = 'zeus.parallelAgents.focus'`
+
+Other branches (status-bar HUD, command palette, tests) should import these constants rather than retype the string IDs. Default location: right-hand **auxiliary bar**, `hideIfEmpty: true`. The activity bar's first slot is intentionally not taken; the view is opened via command palette or by clicking the agent count in the status bar.
+
+## Why no `*.contribution.ts` yet
+
+Registering a view container with no view body, or with a view that only renders "loading…", ships a broken UI as soon as this PR lands. The real registration is paired with the runtime stream in `feat/agent-sdk` (#26), where the view becomes interactive on day one and consumes the constants in `common/parallelAgents.ts`.

src/vs/workbench/contrib/parallelAgents/common/parallelAgents.ts

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+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+// Stable identifiers for the parallel-agents auxiliary-bar view. Exported
+// here (rather than left as strings in the README) so the status-bar item
+// in feat/prompt-cache-hud, command-palette entries, and tests can all
+// import a single source of truth without duplicating literals.
+//
+// The real view registration lives in feat/agent-sdk; it consumes these
+// constants when wiring up ViewContainerRegistry / ViewsRegistry.
+
+export const PARALLEL_AGENTS_VIEW_CONTAINER_ID = 'zeus.parallelAgents';
+export const PARALLEL_AGENTS_VIEW_ID = 'zeus.parallelAgents.list';
+
+export const PARALLEL_AGENTS_COMMAND_NEW = 'zeus.parallelAgents.new';
+export const PARALLEL_AGENTS_COMMAND_FOCUS = 'zeus.parallelAgents.focus';