test(web): strip COTAL_ before the rejection arm's env spread

[davidfarah2003]

Main is red on shard 2 at smoke:suite-ambient-env, and #898 caused it. This is the repair.

What broke

The rejection arm #898 added spawns the web child with an unfiltered spread:

env: { ...process.env, COTAL_WEB_SMOKE_REJECT_HISTORY: "1" }

smoke:suite-ambient-env exists to refuse exactly that, and it named the file on main at
a268c8dbe (run 32977375051, shard 2, job 98205295502):

AssertionError [ERR_ASSERTION]: these suite files spread the ambient environment into a child
without stripping COTAL_ first:
  implementations/web/smoke/bounded-aggregation.smoke.ts

The census's own wording is the reason it matters: whatever runs a suite may be a managed agent
session, so the spread hands the child a live credential and a live broker URL, and the child talks
to the operator's mesh instead of the suite's throwaway one.

The fix

Strip COTAL_ from the copy before the spread, using the idiom the compliant suites already use
(attach-auth-root.smoke.ts:107, control-transport-dial.smoke.ts:51,
discovery-bundle-consumable.smoke.ts:89), then set the one flag the arm needs. Not added to
REVIEWED and not to FROZEN — the census is explicit that FROZEN is a baseline rather than a
place for new entries, and this child genuinely should not inherit connection material.

Verification

• smoke:suite-ambient-env: PASS, with the file now listed under strips COTAL_ before the spread rather than in the assertion.
• smoke:web-bounded-aggregation: 43 passed, 0 failed — the same count as before the change, so
  no cell was lost and fix(web): name rejected history reads #898's rejection cells still hold.

Why it got through

Worth recording rather than just fixing, because this is the second time the same census has caught
the same class from the same direction. #454 did it with console-auth.smoke.ts; this is
bounded-aggregation.smoke.ts. Both times a web smoke gained a child-spawning arm, and both times
the review checked the sibling web suites and not the census that governs child spawning. The
sibling suites cannot catch it — only smoke:suite-ambient-env can, and it lives on a different
shard.

The durable form: a change that gives any suite a new child process must run
smoke:suite-ambient-env before merge, regardless of what else passes.

[davidfarah2003]

APPROVE

Graded exact SHA dff6ddf86893ad27ded23f49cddcaf7fa02d48eb.

Verified:

• pnpm build passes after a frozen-lockfile install.
• smoke:suite-ambient-env passes with implementations/web/smoke/bounded-aggregation.smoke.ts reported under strips COTAL_ before the spread, not REVIEWED or FROZEN.
• Direct child instrumentation with an ambient COTAL_REVIEW_SENTINEL observed exactly {"COTAL_WEB_SMOKE_REJECT_HISTORY":"1"}.
• smoke:web-bounded-aggregation passes 43/0.
• Removing the rejection flag produced exactly two failures, cells 5.1 and 5.2, at 41/2. After restoration both prescribed smokes passed again and the tree was clean.