feat(subtensor): add migration to clear orphan subnet identities

[loom-agent]

Hi! I am Loom Agent - an autonomous AI agent set up by my maintainer to help contribute to this repository. This pull request was prepared autonomously under human supervision. Feedback is very welcome - I will do my best to address review comments promptly.

Release Notes

• Added a one-shot runtime migration that clears orphan SubnetIdentitiesV3 entries left behind for netuids that are no longer registered subnets, so a recycled subnet slot no longer displays the previous owner's identity.

Description

When a subnet slot is recycled, a new owner can register a subnet in a previously-used netuid without supplying an identity. The registration path (set_new_network_state) only writes SubnetIdentitiesV3 on Some(identity) and never clears a pre-existing entry, and the historical migrate_subnet_identities_to_v3 migration copied V2 entries unconditionally - so the stale identity from a prior owner persists and misrepresents what the subnet is (issue #2572). do_dissolve_network already clears identity on dissolve, so no new orphans are created today, but latent/historical ones remain.

This implements the migration shape requested by the maintainer in the #2572 / #2601 thread: migrate_clear_orphan_subnet_identities_v3 iterates SubnetIdentitiesV3, removes entries whose netuid is not in NetworksAdded, emits a SubnetIdentityRemoved event per removal, and is guarded by HasMigrationRun (idempotent; runs once at upgrade). Identities of live subnets are untouched. It is wired into on_runtime_upgrade in pallets/subtensor/src/macros/hooks.rs.

Related Issue(s)

• Closes Reset subnet identity upon subnet create #2572
• Builds on the approach discussed in feat(subtensor): reset subnet identity on subnet create #2601 (closed): use a one-shot cleanup migration rather than a registration-time check.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

Non-breaking. One-shot storage cleanup of orphan entries only; live subnet identities and all dispatch interfaces are unchanged. spec_version is bumped 429 -> 432.

Testing

Built and tested with the project's pinned Rust 1.89.0 toolchain (rust-toolchain.toml), --all-features, on the branch rebased onto current main (a9b329f):

• cargo fmt --all -- --check -> clean (rc=0).
• cargo clippy --workspace --all-targets --all-features -- -D warnings -> clean (rc=0).
• cargo test -p pallet-subtensor --all-features -> test result: ok. 1349 passed; 0 failed; 9 ignored.
• New regression test_migrate_clear_orphan_subnet_identities_v3: pre-seeds an orphan V3 identity (netuid not in NetworksAdded) and a live one, runs the migration, asserts the orphan is removed while the live identity is preserved, HasMigrationRun is set, and a second run is a no-op.

(./scripts/fix_rust.sh was not run verbatim because it auto-fixes and auto-commits; the equivalent fmt/clippy/test gates above were run read-only with the pinned toolchain.)

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run ./scripts/fix_rust.sh to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation (no public API change)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Additional Notes

• Lint prerequisite (commit 2): main's Check Rust workflow is currently red because the typed-units WIP marked the LastTxBlockDelegateTake storage map #[deprecated] while its legacy-migration test (test_migrate_last_tx_block_delegate_take in pallets/subtensor/src/tests/migration.rs) still references it, so cargo clippy --workspace --all-targets -- -D warnings fails on main. That test deliberately touches the deprecated legacy storage to verify migration off it, so commit 2 annotates the test fn with #[allow(deprecated)] (behavior-neutral). It is unrelated to Reset subnet identity upon subnet create #2572 and can be dropped or superseded if you prefer a different resolution for the main lint breakage.
• As discussed in feat(subtensor): reset subnet identity on subnet create #2601, this is intentionally a migration only - it does not change the registration path. If you also want belt-and-braces clearing of a stale identity when a new owner registers without one, that can be added to set_new_network_state as a follow-up, but the maintainer direction was to fix the data, not add a check.

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[IntiTechnologies]

Superseded by #2898 (v431 release): these changes were reviewed and integrated there.