A failed catalog chunk could try every authenticated peer identity. Since each
source owns a fresh transfer deadline, one host could use Sybil identities to
turn a single unavailable chunk into a multi-hour retry sequence.
Count the initial source and cap one chunk at eight distinct peer identities.
Integrity quarantine, transport classification, cancellation, and explicit
user retries retain their existing behavior.
Test Plan:
- `just test` -- passed outside the sandbox; 495 peer tests and all workspace
targets passed.
- `just fmt` -- Rust formatting completed; the recipe then hit the pre-existing
generated `security-report/report.md` Markdown-lint failures.
- `git diff --cached --check` -- passed.
ddidderr
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