Three parts, all mutation-proven.

(i) provider-bundle-check.py gains PREFER_IPV6_CHARMS -- the measured authority,
keyed by CHARM name, carrying the revisions and a re-measure warning -- and
invariant 9 is REPLACED, never deleted:
  9a  prefer-ipv6 on a charm that does NOT declare it FAILS. Asserted on
      PRESENCE, not truthiness: 'prefer-ipv6: false' is the same fatal
      'unknown option' to juju as true.
  9b  on a DECLARING charm it still travels with the v6 legs -- the L3-9
      protection is retained unchanged for those seven.
  9c  arity.
The old text's mechanism claim ("prefer-ipv6 makes HAProxy bind :::port") is
refuted by this session's measurement and is recorded as such in-file.

(ii) render-dc-overlays.py emits the option only for a declaring charm, READING
the set from provider-bundle-check with ast rather than restating it (the same
rule APP_OCTET already uses). render() keeps its purity property: the set is a
PARAMETER and the default REFUSES rather than defaulting to empty, because an
empty set renders a plausible artifact with the option nowhere. Both overlays
re-rendered: exactly SIX lines removed per DC and nothing else -- every vip
string byte-identical, so all v6 legs are retained.

(iii) tests/provider-bundle-check 44 -> 48/48. T43 reproduces the attempt-1
defect; T44 proves presence-not-truthiness; T45 is the positive control; T46
asserts the DIAGNOSIS.

MUTATION PASS -- six mutations, every one killed tests. And one NEW assertion
was found to be DECORATION and was REPLACED rather than kept: T46's first form
could not fail under any mutation, because a non-declaring charm with no option
reaches neither branch. Re-written to catch the fold-9a-into-9b simplification
and re-proven.

Gauntlet ALL GREEN (93); repo-lint 0 fail. The fixed dc0 deploy input now
sweeps CLEAN on option names: 75 assignments, 20 schemas, 0 unknown.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HvCyrwvYTTcDYnRErfMsNf