perf #418: publish landblocks under the meter, not one per streaming tick

Phase-1 measurement (new [publish-timing]/[stream-tick] probe surfaces,
ACDREAM_PROBE_REVEAL_TIMING=1) refuted the ~31 ms-per-admission
hypothesis: the hold runs at ~64 fps with the streaming tick at ~32 Hz,
the whole 625-block window costs only ~500 ms of publication CPU (far
blocks ~0.17 ms, near 2-43 ms), and steady state showed ZERO meter
yields with ~0.22 ms of the 2 ms budget used - yet exactly one block
published per tick against a ~400-deep completion queue.

The real limiter: Runtime's collision-generation activation is a
deliberate two-poll transaction (the first
TryAcquireCollisionPrefixMutationPermission poll parks residents and
refuses by design), and LandblockPresentationPipeline.Advance's metered
arm returned Completed=false on ANY nonterminal commit, which
DrainAndApply treats as end-of-frame. One landblock per 32 Hz tick =
the flat 32/s, with the authored budget ~90% idle.

Fix: the metered arm now uses the same Runtime-owned gate the unmetered
arm and the synchronous CompletePublication API always used
(CanContinueMutationSynchronously). The second poll runs in the same
frame under the same meter, so the unchanged 2 ms elapsed-time ceiling
is now genuinely the authoritative per-frame bound; with any real debt
(live residents parked mid-game, pending withdrawals, dispatch backlog)
publication defers to the next frame exactly as before. No budget
values change, no reveal-gate/readiness change, and the streamed result
is byte-identical - only the frame scheduling of identical operations.

Measured A/B (this binary, two runs): totalMs 12689 / 12734 vs baseline
26728/27395/27503; loaded slope 32/s -> bursts of 100-360/s, 625/625 in
~6-7 s vs ~23 s. The remaining ~12.7 s floor is fully attributed in
docs/ISSUES.md: ~8 s of real budgeted readiness work plus retail's
authored tunnel exit (TunnelContinue 2-5 s + two 1 s fades, golden
constants), so the <12 s acceptance needs a lead decision on the
hold-time budget, not another hidden limiter.

New regression pin:
MeteredLoaded_NonterminalCommitWithoutDebt_CompletesInOneMeteredAdvance.
Gates: Release build 0 errors; App tests 5576/3 skips/0 failed;
Runtime tests 1756/0.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Streaming/LandblockConcretePresentationPipelineTests.cs

@@ -171,6 +171,57 @@ public sealed class LandblockConcretePresentationPipelineTests
         Assert.True(fixture.State.IsLoaded(LandblockId));
     }
 
+    [Fact]
+    public void MeteredLoaded_NonterminalCommitWithoutDebt_CompletesInOneMeteredAdvance()
+    {
+        // #418: Runtime's collision-generation activation deliberately
+        // refuses its FIRST CommitCollisionGeneration poll (the quiescence
+        // boundary parks residents and returns nonterminal). The metered
+        // pipeline used to defer the second poll to the next frame
+        // unconditionally, which serialized the login completion drain to
+        // exactly one landblock per streaming tick (the flat 32 blocks/s
+        // hold). With no cross-cutting debt the second poll must now run in
+        // the SAME metered advance, so a whole publication completes in one
+        // frame when the budget allows it.
+        var calls = new List<string>();
+        ConcreteFixture fixture = Fixture(
+            calls,
+            commitEnvCells: _ => calls.Add("envcell"));
+        var pipeline = new LandblockPresentationPipeline(
+            fixture.Render,
+            fixture.Physics,
+            fixture.Static,
+            fixture.State,
+            fixture.RetirementOwner,
+            onLandblockLoaded: _ => calls.Add("live-recovery"));
+        LandblockStreamResult.Loaded result =
+            Result(Build(Entity(0x80A9B401u)));
+        LandblockStreamCostEstimate estimate =
+            LandblockStreamResultCost.Estimate(result);
+        var budget = new StreamingWorkBudget(
+            TimeSpan.FromSeconds(1),
+            maxCompletionAdmissions: 64,
+            maxAdoptedCpuBytes: 1_000_000,
+            maxEntityOperations: 4_096,
+            maxGpuUploadBytes: 1_000_000,
+            maxGlRetireOperations: 64,
+            destinationReserveFraction: 0.75f);
+        var meter = new StreamingWorkMeter(budget);
+
+        LandblockPublicationAdvance advance = pipeline.PublishLoaded(
+            result,
+            estimate,
+            meter,
+            ensureProgress: true);
+        meter.FinishFrame();
+
+        Assert.True(advance.Completed);
+        Assert.False(pipeline.HasPendingPublication(result));
+        Assert.True(fixture.State.IsNearTier(LandblockId));
+        Assert.Equal(1, fixture.Physics.Diagnostics.CompleteCount);
+        Assert.Equal(1, fixture.Static.Diagnostics.CompleteCount);
+    }
+
     [Fact]
     public void CrossOwnerValidationFailure_BlocksBeforeAnyPresentationMutation()
     {