fix(p2p-10): harden redirect correctness (#671)

[jlon]

Summary

• Close correctness gaps in the redirect path after the data-plane architecture is in place.
• Keep this branch intermediate-only; runtime listener and reader lifecycle safety still land in p2p-11.

Design

• Reject redirects to empty peers and scope cached tickets by request context.
• Keep rollout posture unchanged and avoid mixing in runtime lifecycle changes.

Implementation

• Serve published chunks before persist completes and add pending-fetched visibility glue.
• Refresh provider advertisement on republish and prevent stale ticket reuse across tenant/mtime.

Verification

• Verify there is no stale ticket reuse across tenant or mtime boundaries.
• Verify published chunks remain readable before persist completes and provider refresh works after republish.

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