feat(system-prompt): template-based system prompt builder extension

New @dispatch/system-prompt extension (standard tier):
- Pure parser: [type:name] variables, [if]/[else]/[endif] conditionals,
  negated [if !...], nested blocks, unmatched-tag pass-through.
- Variable resolver (injected adapters): system:time/date/os/hostname,
  prompt:cwd/model/conversation_id, git:branch/status, file:<path> (dynamic).
- Service handle: construct (resolve+persist) + get (cached, cache-safe).
- Default template: persona + AGENTS.md if exists + cwd.
- 52 tests (parser 29, resolver 12, catalog 3, service 8).

transport-contract 0.17.0→0.18.0: SystemPromptTemplateResponse,
SetSystemPromptTemplateRequest, SystemPromptVariable, SystemPromptVariablesResponse.

Design: notes/system-prompt-design.md (caching constraint, compaction
integration, wave plan). 1384 vitest pass.

1 files changed, 31 insertions, 0 deletions

diff --git a/packages/system-prompt/src/catalog.test.ts b/packages/system-prompt/src/catalog.test.ts
new file mode 100644
index 0000000..406455b
--- /dev/null
+++ b/packages/system-prompt/src/catalog.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { getVariableCatalog } from "./catalog.js";
+
+describe("catalog", () => {
+	it("lists all fixed variables", () => {
+		const catalog = getVariableCatalog();
+		const keys = catalog.map((v) => `${v.type}:${v.name}`);
+
+		expect(keys).toContain("system:time");
+		expect(keys).toContain("system:date");
+		expect(keys).toContain("system:os");
+		expect(keys).toContain("system:hostname");
+		expect(keys).toContain("prompt:cwd");
+		expect(keys).toContain("prompt:model");
+		expect(keys).toContain("prompt:conversation_id");
+		expect(keys).toContain("git:branch");
+		expect(keys).toContain("git:status");
+	});
+
+	it("marks the file type as dynamic", () => {
+		const fileVar = getVariableCatalog().find((v) => v.type === "file");
+		expect(fileVar).toBeDefined();
+		expect(fileVar?.dynamic).toBe(true);
+	});
+
+	it("every entry has a description", () => {
+		for (const v of getVariableCatalog()) {
+			expect(v.description.length).toBeGreaterThan(0);
+		}
+	});
+});