tools(sentry): anchor the measurement windows on the gate's rollout instant (#178)

A window that spans the 2026-08-14 14:22Z production rollout contains devices
that could not possibly have run the gate. Its rate is neither a baseline nor a
result, and it prints identically to both. This was not hypothetical: a
`post=08-14T07:00Z..now` window (84% of it pre-rollout) was run against this
script and reported opencode-mobile *rising* to 4.44/h.

`noise-gate-report.mjs` shipped with the same defect built into its default:
`post = now-7d..now` straddles the rollout on every run before 08-21, diluting
the after-rate toward baseline - biased toward grading the gate as ineffective
on exactly the dates the ticket schedules its reads (08-17, 08-21).

- sentry-volume-report: `--since-rollout` reads the instant from the release
  history table in docs/playstore.md (production versionCode >= 150, earliest
  such release, so a later v0.4.15 does not restart the window) and splits
  there. Every window is labelled [pre]/[post]/[mixed]; mixed prints how much
  of it predates the gate, a young post window prints its uptake age, and an
  unparseable table reports "unknown" rather than assuming post.
- noise-gate-report: defaults post to the rollout instant, returns UNGRADED for
  a mixed/unknown post window, and pins the baseline to the documented
  post-box-bot-fix window instead of a 7d lookback that dragged ~22k/mo of
  already-fixed box-bot volume into the org outlook (it read "MISSES by 18,612"
  for a dead reason; now 628/mo, clears).
- before_send == 0 is now reported as expected in a pre/mixed/young window and
  as a failure only after 24h+ of gated production.

Re-probed every server-side lever with a WRITE-scoped token so none of the
answers is a permissions artifact, and corrected the record in docs/analytics.md:
per-key rate limit returns 200 and silently drops the field; error-message
filters return 400 "You do not have that feature enabled" (a plan gate, not
absence - it is the one lever that would reach never-updating installs); spike
protection is not 403-unavailable, it is already enabled everywhere and simply
does not fire on sustained baseline volume.

Co-authored-by: engineer <engineer@macbookpro.lan>

scripts/sentry-volume-report.test.mjs

@@ -0,0 +1,84 @@
+import assert from "node:assert/strict"
+import { readFileSync } from "node:fs"
+import test from "node:test"
+
+import { GATE_FIRST_VERSION_CODE, classifyWindow, gateRollout, parseRolloutHistory } from "./sentry-volume-report.mjs"
+
+const win = (start, end) => ({
+  start: new Date(start),
+  end: new Date(end),
+  hours: (new Date(end) - new Date(start)) / 3_600_000,
+})
+
+const ROLLOUT = new Date("2026-08-14T14:22:00Z")
+
+test("the real docs/playstore.md yields the gate's production rollout instant", () => {
+  const rows = parseRolloutHistory(readFileSync(new URL("../docs/playstore.md", import.meta.url), "utf8"))
+  assert.ok(rows.length >= 2, "release history table should parse")
+  const gate = gateRollout(rows)
+  assert.ok(gate, "a production release >= the gate versionCode must be recorded")
+  assert.ok(gate.versionCode >= GATE_FIRST_VERSION_CODE)
+  assert.equal(gate.at.toISOString(), ROLLOUT.toISOString())
+  assert.equal(gate.version, "v0.4.14")
+})
+
+test("production versionCode is read, not the internal tag-push one", () => {
+  // The bold production code (151) is what reached users; 150 only ever went to
+  // the internal track. Reading column 1 would date the rollout to the wrong row.
+  const rows = parseRolloutHistory(`
+| Version | Internal versionCode | Production versionCode | Production rollout (UTC) | Notes |
+|---|---|---|---|---|
+| v0.4.14 | 150 (run 50) | **151** (run 51) | 2026-08-14 14:22 | gate |
+`)
+  assert.deepEqual(
+    rows.map((r) => [r.version, r.versionCode]),
+    [["v0.4.14", 151]],
+  )
+})
+
+test("a build that never reached production is not a rollout", () => {
+  // No production versionCode and no rollout instant -> it reached no device.
+  const rows = parseRolloutHistory(`
+| v0.4.15 | 152 (run 52) | — | — | internal only |
+| v0.4.14 | 150 (run 50) | **151** (run 51) | 2026-08-14 14:22 | gate |
+`)
+  assert.equal(rows.length, 1)
+  assert.equal(gateRollout(rows).version, "v0.4.14")
+})
+
+test("a later gated release does not re-start the measurement window", () => {
+  const rows = parseRolloutHistory(`
+| v0.4.15 | 152 (run 52) | **153** (run 53) | 2026-08-20 09:00 | later |
+| v0.4.14 | 150 (run 50) | **151** (run 51) | 2026-08-14 14:22 | gate |
+`)
+  assert.equal(gateRollout(rows).at.toISOString(), ROLLOUT.toISOString())
+})
+
+test("the mistake this guard exists for: a 'post' window that predates the rollout", () => {
+  // Actually run on 2026-08-14: --window post=07:00Z..now, rollout was 14:22Z.
+  // 84% of it was pre-gate traffic, and it reported opencode-mobile *rising*.
+  const c = classifyWindow(win("2026-08-14T07:00:00Z", "2026-08-14T15:41:00Z"), ROLLOUT)
+  assert.equal(c.phase, "mixed")
+  assert.ok(c.gatedFraction < 0.2, `only ${(c.gatedFraction * 100).toFixed(0)}% is post-gate`)
+})
+
+test("clean pre/post windows classify, and the boundary belongs to neither side twice", () => {
+  assert.equal(classifyWindow(win("2026-08-13T14:22:00Z", "2026-08-14T14:22:00Z"), ROLLOUT).phase, "pre")
+  const post = classifyWindow(win("2026-08-14T14:22:00Z", "2026-08-15T14:22:00Z"), ROLLOUT)
+  assert.equal(post.phase, "post")
+  assert.equal(post.gatedFraction, 1)
+  assert.equal(post.postHours, 24)
+})
+
+test("a fresh post window reports its age, so before_send == 0 is not read as failure", () => {
+  const c = classifyWindow(win("2026-08-14T14:22:00Z", "2026-08-14T15:43:00Z"), ROLLOUT)
+  assert.equal(c.phase, "post")
+  assert.ok(c.postHours < 24, "under a day of uptake cannot certify anything")
+})
+
+test("no known rollout is 'unknown', never silently 'post'", () => {
+  // Absence of the record must not be reported as a clean post-gate reading.
+  assert.equal(classifyWindow(win("2026-08-14T14:22:00Z", "2026-08-15T14:22:00Z"), null).phase, "unknown")
+  assert.equal(gateRollout(parseRolloutHistory("no table here")), null)
+  assert.equal(gateRollout(parseRolloutHistory("| v0.4.13 | 148 | **149** | 2026-08-14 09:20 | pre-gate |")), null)
+})