fix(coccontainer): build coc in serve loop and fail fast when dashboard template is missing

[kah279]

Problem

Running ./scripts/coccontainer-serve-loop.ps1 on a freshly cloned repo says the dashboard is at
http://localhost:5000, but every browser request hangs forever — the process binds the port but no GET /
response is ever sent.

Root cause

The coccontainer GET / handler renders the dashboard HTML by require()-ing coc's compiled
dist/server/spa/html-template.js at runtime. That file is produced by coc's build step — but the serve-loop
scripts only built forge and coccontainer, never coc. So on a fresh checkout the template was missing and
the require threw.

The throw happened after the handler called res.writeHead(200, ...), so the outer try/catch saw
headersSent === true and silently dropped the response, leaving the socket open until the client timed out.

Fix

Two layered changes, each useful on its own:

1. Scripts — build coc in the loop

scripts/coccontainer-serve-loop.ps1 and scripts/coccontainer-serve-loop.sh now build the full chain forge → coc-client → coc → coccontainer before serving (matching what coc:link does for the coc serve loop). This
guarantees dist/server/spa/html-template.js exists before the container ever tries to render it.

2. Server hardening — fail fast & observable

packages/coccontainer/src/server/index.ts:

• Adds ContainerServerOptions with injectable htmlRenderer and skipHtmlPrecheck seams so the failure
  modes are testable.
• Eager probe at startup: createContainerServer invokes the renderer once before binding the port. If the
  template can't be loaded, the process exits with an actionable error ("Build coc first: \npm run build` in
  packages/coc`") instead of binding :5000 and hanging requests.
• Reordered GET / handler: dashboard HTML is now computed before res.writeHead(200). Any future
  render failure lands in the existing !headersSent catch and produces a clean 500 JSON instead of a hung
  socket — preserving observability for the next time something breaks.

3. Drive-by fix to keep coc building

packages/coc/src/server/spa/client/react/contexts/ContainerAgentContext.tsx was importing/calling
setServerAuthAgents, a symbol deleted by the earlier devtunnel-token-auth revert (#…). That broke npm run build -w packages/coc with No matching export ... for import "setServerAuthAgents", which would have
prevented the script fix above from unblocking anything. Removed the dead reference.

Tests

New file: packages/coccontainer/test/server/dashboard-html.test.ts — 4 Vitest cases:

1. Happy path: server starts and GET / returns the dashboard HTML.
2. Eager probe failure: a broken renderer causes createContainerServer to throw at startup with the
   actionable message (no port is bound).
3. Request-time render failure: a renderer that succeeds at probe but throws on a later request returns
   500 application/json, not a hung socket.
4. Actionable startup message: the thrown error mentions running npm run build in packages/coc.

All 48 coccontainer tests pass on Windows. npm run lint is clean (0 errors).

Verification

• Fresh clone → ./scripts/coccontainer-serve-loop.ps1 → http://localhost:5000 renders the dashboard
  immediately.
• Force-deleted packages/coc/dist and re-ran the script → coc gets rebuilt before serve.
• Manually broke the html-template import → server now exits at startup with the actionable error rather than
  binding :5000 and hanging.

Files changed

.../react/contexts/ContainerAgentContext.tsx | 4 +- packages/coccontainer/src/server/index.ts | 74 ++++++++---
.../test/server/dashboard-html.test.ts | 150 +++++++++++++++++++++ scripts/coccontainer-serve-loop.ps1 | 15 ++-
scripts/coccontainer-serve-loop.sh | 10 +- 5 files changed, 231 insertions(+), 22 deletions(-)