fix: load balancer admits through its pool instead of passing everything

[nawazish2]

What this changes

An lb now takes the engine's default serve path, so capacity, instances and queueLimit go through ordinary slot and queue discipline. Closes #52.

Why

onAdmit returned passthru, which left admission before either check ran. A balancer sized for two concurrent calls carried ~3000 rps, waiting stayed 0, and an autoscaler writing instances moved a number that bound nothing.

The inspector already said the pool was real. The engine now matches that.

Verification

client(3000 rps) -> lb -> service(64 slots x 8), lb serviceMs: 5, 30 simulated seconds. Ceiling is capacity * instances * (1000 / serviceMs).

Before (passthru):

instances  capacity  queueLimit   ceiling   throughput   in flight   queued   shed
        1         2           4     400 rps     2965.6          10        0      0
        1         2        4096     400 rps     2965.6          10        0      0
       12         2           4    4800 rps     2965.6          10        0      0
        1        64           4   12800 rps     2965.6          10        0      0

After (serve):

instances  capacity  queueLimit   ceiling   throughput   in flight   queued   shed
        1         2           4     400 rps      400.0           2        4   2660
        1         2        4096     400 rps      400.0           2     4096   2660
       12         2           4    4800 rps     2963.3          14        0      0
        1        64           4   12800 rps     2953.3          13        0      0

This changes behaviour for every design with an lb in it. Default lb sizing (256 slots at 0.5ms) still sits at ~512k rps, so existing presets stay under 2% errors.

• bun run test — 914/914 tests pass
• bun run typecheck and bun run lint pass
• bun run build passes
• Screenshot attached, if anything visual changed — n/a, engine-only

Made with Cursor

[vercel]

@nawazish2 is attempting to deploy a commit to the whoarrryou's projects Team on Vercel.

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[xevrion]

Checked all five lb presets, none of them move. LGTM, thanks!