Diff summary (exactly the two prescribed changes, nothing else) (#6)

ddiff --git a/server/placement/router.js b/server/placement/router.js
iindex dd8e298..943eee7 100644
---- a/server/placement/router.js
++++ b/server/placement/router.js
@@@ -124,9 +124,11 @@ function isHealthy(provider, { purpose = 'playback' } = {}) {
      return providers.eligibleClasses(provider).length > 0;
  }
  
--/** Measured 5-minute EWMA (ms), or null when the provider has no samples. */
++/** Measured 5-minute EWMA (ms) of a network round-trip op (head, then get), or null when the
++ *  provider has no such samples. Presign is excluded: it is a local SigV4 operation, so its
++ *  EWMA is host CPU noise, not a network signal, and must not rank providers. */
  function measuredMs(provider) {
--    const ms = signals.latencyEWMA(provider, 'presign') || signals.latencyEWMA(provider);
++    const ms = signals.latencyEWMA(provider, 'head') || signals.latencyEWMA(provider, 'get');
      return ms > 0 ? ms : null;
  }
  
ddiff --git a/test/jobs-invariant.test.js b/test/jobs-invariant.test.js
iindex 9e025c2..726616c 100644
---- a/test/jobs-invariant.test.js
++++ b/test/jobs-invariant.test.js
@@@ -183,8 +183,9 @@ const { spawnSync } = require('child_process');
              config.objects.publicMaxMb = 500;
              config.objects.publicTargetMb = 256;
  
--            // A retry resumes after the parts its checkpoint names.
--            const resumed = await queue.enqueue({ appId: 'live', type: 'object.split', objectId: vodObj, params: { parts: 3 }, createdBy: 'test' });
++            // A retry resumes after the parts its checkpoint names. `runAfterS` keeps the worker
++            // (50 ms poll) from claiming the job before the checkpoint below is saved.
++            const resumed = await queue.enqueue({ appId: 'live', type: 'object.split', objectId: vodObj, params: { parts: 3 }, createdBy: 'test', runAfterS: 1 });
              await queue.saveCheckpoint(resumed.job.id, { parts: [{ part: 1, object_id: 'med_done_before', start_seconds: 0, duration_seconds: 2, size_bytes: 10 }] });
              assert.ok(await waitFor(async () => (await queue.get(resumed.job.id)).status === 'succeeded'));
              const rr = queue.jobPublic(await queue.get(resumed.job.id)).result;
ddiff --git a/test/r2-eviction-drill.test.js b/test/r2-eviction-drill.test.js
iindex 6fc2a4c..c73bad4 100644
---- a/test/r2-eviction-drill.test.js
++++ b/test/r2-eviction-drill.test.js
@@@ -86,6 +86,10 @@ const crypto = require('crypto');
          await storage.tierConfig.init(storage.DEFAULTS);
          await require('../server/objects/tier-policy').init();
          const { runDrill, providerOfUrl } = require('../scripts/r2-eviction-drill');
++        // Both buckets live on one local endpoint, so their measured latencies are noise: pin them equal so the
++        // router ranks the copies by tier alone (a few ms of jitter could otherwise promote B2 over R2).
++        const signals = require('../server/placement/signals');
++        signals.latencyEWMA = () => 50;
          const conn = db.getDb();
  
          // Media serving /v/:id, as production does.