[portlandhodl]

Summary

Adds a cargo-fuzz crate with four targets and a dedicated Fuzz workflow.

Targets

• changeset_roundtrip: generates mostly-valid change sets, persists them, reloads, re-persists the full snapshot, and asserts persist/load idempotence. Structurally rejected change sets must roll back cleanly.
• corrupt_rows: starts from a fully populated store and mutates tx, txout, anchor_tx, block, keychain, and network columns with arbitrary blobs, integers, and text. Every load must return Ok or a typed error, never panic.
• anchor_identity: persists anchors for the same block/transaction with different confirmation times and heights and asserts all survive, including stale observations.
• descriptor_validation: injects multipath/hardened descriptors (and arbitrary bytes) into keychain and asserts UnsupportedDescriptor rather than a panic.

CI

.github/workflows/fuzz.yml runs all four targets:

• 90 seconds per target on pull requests and pushes to master.
• 300 seconds per target on the weekly schedule.
• Lints and formats the fuzz crate with nightly, builds each target, and uploads artifacts on failure.

Verification

• cargo test --all-targets / cargo clippy --all-targets -- -D warnings
• cargo +nightly check/clippy --manifest-path fuzz/Cargo.toml --all-targets
• Ran every fuzz target locally for 15–20 seconds with no findings.

Depends on

Stacked on #29; base is fix/descriptor-id-validation.