[docwilde]

Empty or whitespace-only memory replacements could silently delete an entry while reporting success. Reject them in the Rust direct and internal mutation paths and Python compatibility API, preserving the original memory, provenance, and sync history; native model/derived requests are refused before staging. Explicit removal remains supported.

Closes #132.

Also add an end-to-end regression test for the historical recovery implemented in v0.62.7 (related to #112): authenticated peer replay retains signed quarantine, banks its cursor, matches portable state and bundles, and remains idempotent. Unsigned hub copies remain unapplied.

Validation:

• Rust memory tests: 12 passed; native CLI tests: 13 passed.
• Historical belief peer replay integration test: passed.
• Python write-gate, pending-safety, sync-merge, and portable project-key tests: 155 passed.
• Broader local checks reproduced 11 Rust library failures and one native interoperability failure on the untouched base revision as well.
• git diff --check passed.