feat(subtensor): split InsufficientBalance into TAO and Alpha variants

[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

• Changed the shared InsufficientBalance dispatch error into two distinct errors, InsufficientTaoBalance (TAO) and InsufficientAlphaBalance (Alpha stake), so SDK consumers and callers can tell which asset was insufficient. Chain-extension ABI is unchanged (both still surface as code 12).

Revision notes (addressing code-review feedback)

This update rebases the branch onto current main and collapses it into a single self-contained commit to address the review blockers:

• Source change is unambiguous (was flagged as missing). The variant InsufficientAlphaBalance is defined in pallets/subtensor/src/macros/errors.rs (appended, so no existing error index shifts) and is wired into the Alpha balance guard of BalanceOps::decrease_stake (pallets/subtensor/src/lib.rs). decrease_stake is a trait method of subtensor_runtime_common::BalanceOps, so the regression test brings the trait into scope (use subtensor_runtime_common::BalanceOps;) to call it. The earlier multi-commit history had a spec-only commit with no source diff, which made the change look absent when viewed one commit at a time; the single commit removes that ambiguity.
• spec_version is now a single clean bump. Current main is at spec_version: 430; this commit sets it to 431 (main + 1). The earlier 429->430 then 430->431 two-commit churn is gone.
• transaction_version is intentionally not bumped. This repo keeps transaction_version: 1 across every spec bump (it is still 1 at spec_version: 430). Renaming a dispatch error in place (index preserved) and appending a new variant change pallet metadata, which is covered by the spec_version bump, but do not change extrinsic/call encoding, so transaction_version is left unchanged per repo convention and Substrate semantics.
• Breaking-change acknowledgement. Per the issue, InsufficientBalance is renamed in place to InsufficientTaoBalance. The numeric index is preserved, so index-based clients are unaffected; only string-based metadata consumers must handle the new names. spec_version is bumped accordingly.
• The obsolete #[allow(deprecated)] prerequisite commit was dropped: current main already annotates the legacy-migration tests that touch the deprecated LastTxBlockDelegateTake storage, so it is no longer needed on this branch.

Description

The single Error::InsufficientBalance was returned for both TAO balance checks and Alpha stake checks, so a caller that hit it could not determine which asset was short without extra probing (issue #1960). This splits it:

• The existing variant is renamed in place to InsufficientTaoBalance (its enum position is preserved, so the numeric indices of the variants after it do not shift).
• A new InsufficientAlphaBalance variant is appended for the one Alpha-balance call site, BalanceOps::decrease_stake (pallets/subtensor/src/lib.rs).
• The four TAO-side call sites in coinbase/tao.rs now use InsufficientTaoBalance.
• The chain-extension error mapping (chain-extensions/src/types.rs) maps both new names to the existing Output::InsufficientBalance ABI code (12); other pallets' own InsufficientBalance (swap, crowdloan) still maps there too, so ink!/EVM contracts are unaffected.

Related Issue(s)

• Closes Separate pallets/subtensor/src/macros/errors.rs:InsufficientBalance to two type of errors. #1960
• Differs from the prior attempt Fix: Issue #1960 - Refactor InsufficientBalance error #2325 (closed, no review): this keeps the renamed variant in place to preserve the error indices after it and maps both new errors to the existing chain-extension ABI code (12), where Fix: Issue #1960 - Refactor InsufficientBalance error #2325 proposed unrelated NotEnoughBalanceToPayFee/NotEnoughBalanceToPayStake names.

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

The pallet error variant InsufficientBalance is renamed to InsufficientTaoBalance and a new InsufficientAlphaBalance variant is appended (prescribed by #1960). The numeric index of the renamed variant is unchanged, but string consumers of the metadata (e.g. SDKs matching the error name) must handle the new names. spec_version is bumped to 431. The chain-extension ABI is unchanged.

Testing

Verified statically against current main:

• InsufficientAlphaBalance is defined in macros/errors.rs; decrease_stake returns it from the Alpha guard (lib.rs), reached via the BalanceOps trait the test imports; the chain-extension maps both new names to ABI code 12.
• The pallet-subtensor source in this commit is byte-identical to the previously verified version (same change set), rebased onto current main with no conflicts in the touched files; the only differences versus the prior build are the dropped obsolete lint prerequisite (already present on main) and the consolidated single spec_version bump.

Runtime gate output for this exact HEAD was not obtainable in this environment: the build VM was unreachable during this revision and fork-PR CI does not auto-run Actions without maintainer approval (0 check-runs at the time of writing). The project check-rust workflow (cargo fmt --check, cargo clippy --workspace --all-targets --all-features -- -D warnings, cargo test -p pallet-subtensor --all-features) is the authoritative gate; the prior build of this identical pallet logic passed fmt, clippy, and 1349 passed; 0 failed; 9 ignored. I will address any CI failures as soon as the workflow runs.

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 (equivalent read-only fmt/clippy gates were run on the prior identical build; CI will confirm for this HEAD)
• I have made corresponding changes to the documentation (no docs reference the error name)
• 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

• The in-place rename (vs. delete+append) is deliberate to avoid shifting the error indices after this variant. Exposing the distinction at the chain-extension Output ABI (a new code instead of collapsing both to code 12) is a larger ABI decision left to the team.

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[IntiTechnologies]

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