test: remove non-enforcing snapshot drift CI step (Closes #415)

[Nife-tanny]

Overview

Path B — Remove it.

Resolves GitHub issue #415 by removing the non-enforcing "Snapshot drift detection" step from CI rather than half-committing to a snapshot baseline that cannot exist in this repo today.

Why Path B (not Path A)

Investigation of the current state revealed that the snapshot step was pure fiction — it never printed its advice, could never fail, and there is no snapshot-golden mechanism in the codebase to enforce:

1. No snapshot mechanism exists in the code. scripts/update_snapshots.sh sets SNAPSHOT_UPDATE=1, but no Rust test ever reads that env var. There is no insta, no .snap reader/writer, and no golden-file harness anywhere in contracts/src/. The contracts/test_snapshots/ directory it targets does not exist anywhere in the repo.

2. The directory is gitignored and thus cannot be committed. contracts/test_snapshots/ is listed in .gitignore. Even if a generator existed, emitted fixtures would never be tracked, so there is no committable baseline — and committing a "verified current" one is impossible because no generator exists to produce it.

3. The CI step is a total no-op. Its guard (if [ -d contracts/test_snapshots ] && ls .../*.snap) is always false (the directory never exists), so the step always printed only "No snapshot golden files to check." It has never printed the drift advice it was written to print, and never failed.

4. Nobody owns it. The single commit that introduced it (e73bb77 "Add snapshot policy and update script for snapshot management") added a CI message + docs + a script, but no implementation and no fixtures, and nothing was ever committed afterward (contracts/test_snapshots/ remains empty/absent).

Path A would have required building an entire new snapshot-testing framework from scratch (a real generation harness, deciding what to capture, unwiring the gitignore, and a maintained baseline) — far beyond "enforce this existing step," and the issue explicitly asks for the honest choice rather than defaulting to A because it "sounds more thorough." There is no current baseline to commit, so Path B (remove the misleading step) is the correct and honest resolution.

What was removed

• .github/workflows/ci.yml — removed the Snapshot drift detection step from the rust-test job (lines 59–71). Standalone step; no other job/step greps its output, and ci-success does not reference it. Job ordering, caching, and downstream steps are unaffected.
• scripts/update_snapshots.sh — removed. Orphaned tooling that only existed to support the dead step; grep confirmed no other active script references it.
• CONTRIBUTING.md — removed the "Snapshot Tests" section describing the non-existent golden-file workflow.
• .github/PULL_REQUEST_TEMPLATE.md — removed the "Snapshot policy" checklist section.
• README.md — removed stale references to contracts/test_snapshots/ (directory tree entry, "NOT Committed" list, git-status-check note/comment).

.gitignore's contracts/test_snapshots/ entry was left in place (inert but harmless; kept to minimize scope).

Reinstate real snapshot testing later

A future maintainer who wants real drift detection should build an actual snapshot harness — e.g. integrate insta into contracts/src/tests/, capture storage/event output from the existing test-utils scenarios, remove the contracts/test_snapshots/ entry from .gitignore so fixtures can be committed, add a SNAPSHOT_UPDATE-style regeneration path that the tests actually honor, and wire a hard-failing diff check into CI.

Verification

• contracts YAML (ci.yml) validated as valid YAML (js-yaml).
• Zero Rust source files and zero Cargo files were modified — verified via git diff --name-only origin/main...HEAD (empty for *.rs/Cargo.*). This change is CI config, docs, the PR template, and the deletion of a dead bash script.

Local verification of standard commands

• cargo fmt --all -- --check: fails (pre-existing) with an identical 4772-line diff on both origin/main and this branch. This is a pre-existing repository condition unrelated to this change — confirmed by running it in a clean worktree of origin/main.
• cargo test --workspace --locked: could not complete locally due to a rustc compiler ICE (internal compiler error) while compiling dependency build scripts (proc-macro2, zmij) under the local Windows x86_64 + rustc 1.97.1 toolchain. This is a local environment/toolchain limitation that occurs before any of the repo's own code is compiled; it is unrelated to this change (which modifies no Rust/Cargo files) and would occur identically on the base branch. CI runs on ubuntu-latest and is unaffected.

No new failures were introduced by this change; the pre-existing cargo fmt failure and the local toolchain ICE are flagged above and left untouched.

Closes #415