feat(agentstack): add @logicsrc/agentstack coordination module

AgentStack is the LogicSRC module for portable agent, task, payment, and
reputation coordination across Profullstack apps. Reference implementation of
the `agentstack` capability in the Profullstack Shared AppKit OpenSpec.

- packages/agentstack: DID helpers (did:coinpay:user/agent), DidTask model +
  lifecycle, AgentStack in-memory coordinator (agents, tasks, delegation,
  events), and a validated LogicSRC plugin definition. 9 vitest cases.
- Wire @logicsrc/agentstack into the root build chain (after plugin-core).
- docs/agentstack.md + mention in openspec-comparison.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/agentstack/README.md

@@ -0,0 +1,67 @@
+# @logicsrc/agentstack
+
+AgentStack is the LogicSRC module for **portable agent, task, payment, and reputation
+coordination** across Profullstack microsaas apps (sh1pt, uGig, qaaas.dev, crawlproof,
+commandboard.run, coinpayportal, logicsrc, intr0s).
+
+It is the reference implementation of the `agentstack` capability in the Profullstack
+Shared AppKit OpenSpec (`profullstack-web/openspec/specs/agentstack`).
+
+## What it provides
+
+- **DID helpers** for CoinPay-linked identities: `userDid`, `agentDid`, `makeDid`, `parseDid`
+  (`did:coinpay:user:123`, `did:coinpay:agent:abc`).
+- **`DidTask`** — a portable task model with a defined status lifecycle
+  (`pending → queued → running → blocked → complete | failed | cancelled`) that can bind to
+  payment, escrow, and reputation events.
+- **`AgentStack`** — an in-memory coordinator that registers agents, tracks tasks, records
+  delegation grants, and emits coordination events. Storage backends can wrap the same API.
+- **`agentStackPlugin`** — a LogicSRC `PluginDefinition` (validated against the plugin
+  manifest schema) exposing AgentStack as a coordination plugin with routes, events,
+  permissions, and a TUI panel.
+
+## Usage
+
+```ts
+import { AgentStack, userDid, agentDid } from "@logicsrc/agentstack";
+
+const stack = new AgentStack();
+const owner = userDid("123");
+
+stack.registerAgent({
+  did: agentDid("abc"),
+  name: "Build Agent",
+  sourceApp: "commandboard.run",
+  supportedProtocols: ["logicsrc/1"]
+});
+
+const task = stack.createTask({ ownerDid: owner, sourceApp: "sh1pt.com", title: "Ship build" });
+stack.assignTask(task.id, agentDid("abc"));
+stack.updateTaskStatus(task.id, "running");
+stack.updateTaskStatus(task.id, "complete", { reputationEventId: "rep_1" });
+```
+
+## Cross-app identity
+
+Each app keeps a local `users.id` and links it to a CoinPay DID, giving cross-app identity
+without shared cookies or one global account database:
+
+```txt
+sh1pt.users.id -> did:coinpay:user:123
+ugig.users.id  -> did:coinpay:user:123
+```
+
+## Environment
+
+```txt
+AGENTSTACK_API_URL
+AGENTSTACK_API_KEY
+COINPAY_API_BASE_URL
+```
+
+## Scripts
+
+```bash
+npm run build   # tsc -> dist
+npm test        # vitest
+```