test(loadharness): retain raw resource samples; record findings F4 and the discarded run

HarnessRunResult now carries every ResourceSample, not just the window summaries.
Motivated by finding F1: the definitive run recorded ZERO gen-2 collections across
45M events, so a positive least-squares heap slope cannot be told apart from
gen-2 garbage that was simply never collected. The summary alone cannot settle
that; the series can. The reported run predates this field -- noted as such in the
results doc rather than implied otherwise.

Also records:
  - the second full-scale run was DISCARDED, not reported: a verification build
    overlapped the start of its measurement window, and a contaminated measurement
    is not evidence.
  - finding F4, a pre-existing test-isolation flake in
    QueueDepthGaugeTests.Gauge_TracksBufferedDepth_AcrossEnqueueDrainAndPark
    (fails in a full-suite run, passes in isolation -- shared static gauge carrying
    state across tests). It cannot originate here: this branch changes zero src/
    files vs its base 986e6e7a. Left unfixed deliberately; filed for separate triage.

Verified: full slnx build clean; SiteRuntime 604/604, Communication 691/691 pass;
TargetScaleHarnessSmokeTests passes (78s).

docs/plans/2026-08-15-target-scale-load-test-results.md

@@ -26,9 +26,13 @@
 | Measurement window | 20 minutes steady state, after a 2-minute settle |
 | Total wall time | 1,510 s (~25 min) |
 
-Two independent full-scale runs were executed. **Run 1** is the primary dataset.
+**One clean full-scale run is the dataset reported here.** A second run was started to
-**Run 2** re-ran the identical protocol with raw per-sample resource capture added
+add raw per-sample resource capture (sharpening finding F1), but a verification build
-(the only harness change between them) to resolve the memory question in §4.
+overlapped the start of its measurement window; it was **discarded rather than
+reported**, per the rule that a measurement contaminated by concurrent load is not
+evidence. The raw-sample capture it was meant to exercise is now in the harness
+(`HarnessRunResult.ResourceSamples`) and will be present in any future run, including
+the 1-hour run in §7 — the run reported below predates that field.
 
 ---
 
@@ -224,6 +228,23 @@ limit on burst absorption. The probe paces at 2,000 events/s to isolate the vari
 under test; the shared stage's own capacity is separately covered by
 `SiteStreamThroughputTests`.
 
+### F4 — Pre-existing test-isolation flake in `QueueDepthGaugeTests` (Low, not introduced here)
+
+Noticed during this work package's verification pass, recorded so it is not later
+mistaken for a regression from the load-harness branch.
+
+`StoreAndForward.Tests.QueueDepthGaugeTests.Gauge_TracksBufferedDepth_AcrossEnqueueDrainAndPark`
+**fails in a full-suite run** (`Expected: 0, Actual: 2`, `QueueDepthGaugeTests.cs:116`)
+but **passes when run in isolation** — the signature of a shared static gauge carrying
+state across tests, i.e. an ordering dependency rather than a product defect.
+
+It cannot originate from this branch: the branch changes **zero `src/` files** relative
+to its base (`986e6e7a`), and both the StoreAndForward source and its test project are
+byte-identical to that base. Left unfixed deliberately — out of scope for a measurement
+work package, and the brief was explicitly not to attempt unrelated fixes. Worth a
+separate triage alongside the pre-existing `SandboxTests` timing pin already recorded as
+residual 6 of the arch-review remediation execution log.
+
 ---
 
 ## 5. What this does *not* prove