fix: fix deep sensitive redaction

[ccharly]

Ancestor branches were still able to keep a reference to the original data that was not redacted, resulting in potentially leaking the sensitive data using custom failure reporting.

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Note

Medium Risk
Touches sensitive-data redaction in validation error branches; incorrect ancestor patching could still leak secrets or over-redact, but scope is limited to withRedactedBranch and covered by new tests.

Overview
Fixes a leak in withRedactedBranch where sibling-field validation failures only redacted the immediate parent in failure.branch, while ancestor branch entries still held the original nested object references (so secrets could appear via e.g. branch[0].account.secret).

The redaction logic now finds the parent in the branch, shallow-redacts sensitive keys on that entry, then walks upward through each ancestor—matching the child by reference (===) and swapping in the already-sanitized child—so every branch level reflects redacted nested data.

Adds validation fixtures for one- and three-level nesting to assert fully redacted branches on sibling literal failures.

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