chore(agent): commit the machine tier and the doctrine text the checkout was already running

Landing blocker for #61 and #63: the deployment checkout is 12 commits behind and
`merge --ff-only` refuses while tracked paths are dirty. Discard is not available here
(workspace policy: no `checkout`/`stash` on shared state), so the dirt is committed.

- `agent/APPEND_SYSTEM.md`: the point-of-use / one-work-log / PR-link doctrine, already
  byte-identical to `origin/main` (`cmp` against the trunk blob: no difference). No new
  prose — the commit exists so the trunk merge can proceed.
- `agent/config.yml` and `agent/managed-skills/**`: the machine-live tier the heartbeat
  owns (AGENTS.md § Live-sync tiers).

`ALLOW_SECRETS=1` was used, deliberately and after auditing the staged diff by hand: the
only credential-shaped strings in it are two copies of `AKIA0000000000000EXAMPLE` — the
inert all-zero AWS example id — and they appear inside the two skill pages that teach
that exact placeholder shape. This checkout is still running the pre-#61 hook; the merged
gate (value-scoped placeholder filter, `71601f7`) exempts this value, so the refusal
dies with this landing. No `--no-verify` was used: the gate ran and its verdict is
recorded here.

Refs #61

agent/managed-skills/rng-pool-sweep-blackbox-test/SKILL.md

@@ -0,0 +1,39 @@
+---
+name: rng-pool-sweep-blackbox-test
+description: "Prove membership/absence in a randomly sampled pool (epithets-style) from black-box tests: prime-cycled Math.random sweeps every index; pool-first probe for setting precedence."
+---
+
+# Deterministic pool sweeps for random-sampling black-box tests
+
+When a built bundle samples uniformly at random from a curated pool (epithet-style) and tests must prove a setting admits/excludes whole classes of pool entries, do NOT write probabilistic sampling tests. Two proven designs:
+
+## 1. Full-pool sweep (class membership, distinct counts)
+
+In the test driver (the process that imports the built bundle), before firing utterances:
+
+```ts
+let seed = 0;
+Math.random = () => (seed++ % PRIME) / PRIME; // PRIME > pool size, e.g. 1009
+```
+
+The extension calls `Math.random()` at speak time, so the patch applies regardless of import order. Picks are `floor(random * poolSize)`; with N=PRIME samples the step is `< 1`, so **every index of every pool ≤ PRIME is visited exactly once**. Observable per-utterance text (e.g. the fixture server logs the synthesized `input=`) then reveals the entire sampling pool:
+
+- distinct picks == pool size exactly (pin the total only if it is itself law);
+- a sentinel name from class X appears / must never appear per mode — deterministic, zero flake;
+- absence proofs are exhaustive, not lucky.
+
+Drive one narration per iteration and gate the loop on the fixture's call counter advancing (`while (speechCount() < before + expected) await nap(2)`), otherwise typed/coalescing paths collapse iterations and counts drift.
+
+**Wall-clock budget:** one sweep ≈ 20–40 s per pool; bats serializes and jobs cap at 600 s — run at most two sweeps per backgrounded bats `-f` selection, or launch full suites with `timeout: 0`.
+
+## 2. Pool-first probe (setting precedence, milliseconds)
+
+With the same patched RNG, the FIRST pick is `pool[0]`. Run each config mode with exactly one utterance and compare the first spoken name:
+
+- mode-A setting vs env-mode-A → equal (settings key honored);
+- env-X overriding file-Y → equals env-X's pick (precedence law);
+- pick strings are pool literals that live in exactly one class (e.g. `comrade operator`).
+
+Avoid: regex scans over spoken text (possessives/compounds false-fire), probabilistic "absent in 300 samples" tests (flake floor unless the block is contiguous), and reading source internals (white-box).
+
+Red-first check: the sweep test for a not-yet-filtered pool must fail by SPEAKING the forbidden sentinel — if a "new mode" test passes pre-implementation, the probe accidentally tautologized (e.g. old pool[0] == new pool[0]); pick probe literals whose values differ between old and new behavior. Beware bats `setup()` rebuilding the bundle per test file: a long first sweep lets mid-session src edits leak into later tests' "red" proof — prove red from a pristine tree before implementing.