test(marketplace): pin the agent detail page's load path

[philmerrell]

What

Adds agent-detail.page.spec.ts — the file whose absence let the phase 3 bug fixed in #740 reach users. AgentDetailPage had no spec at all, so a page that rendered "Failed to load this agent." with no HTTP request behind it looked fine to CI.

Five tests over the load path:

• requests the agent the router bound to id
• does not show the error banner when the read succeeds
• asks for runnability separately, for the same id
• shows the error banner when the read actually fails
• keeps the page when only runnability fails

The two that would have caught the original bug assert that AgentApiService.getAgent is called with the bound id, and that the banner is absent on the happy path — deliberately not assertions about the rendered agent, because a zero-request page is what the bug actually produced.

The load-bearing part

⚠️ The component is routed through RouterTestingHarness with provideRouter(routes, withComponentInputBinding()) rather than constructed directly. That is not ceremony: id is an input.required that the router sets after construction, so handing it in at construction time makes every assertion here pass against the broken code too.

Verified both ways — red against the constructor form (getAgent called 0 times), green against the fix.

Please keep that shape if this spec is ever refactored; a TestBed.createComponent with inputs pre-supplied silently stops testing the thing that broke.

Services are stubbed via DI tokens rather than vi.mock, per the repo convention on cross-spec mock pollution.

Verification

npm test (i.e. ng test — there is no standalone vitest config, so a bare npx vitest run fails wholesale and is not the right invocation):

• 137 files, 1565 tests — the 5 new tests pass, against develop with fix(marketplace): the agent detail page never loaded its agent #740 merged
• The only failures in the run were the 6 known load-dependent timeouts in agents/agent-form/agent-form.page.spec.ts, which are unrelated and pre-existing

Depends on

#740 (merged) — the ngOnInit fix these tests pin.

Deploy

None. Test-only; no runtime code touched.

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