fix(ci): remove invalid hashFiles() job-level guard in nightly.yml

hashFiles() is not available at the job-level if: condition — it runs
before actions/checkout so the workspace is empty and GitHub Actions
rejects it as an unrecognized function. The guard was a placeholder
for Story 6.5 which has since landed; the feature_check step already
gates all subsequent steps cleanly.

Author: valentynkit

.github/workflows/nightly.yml

@@ -1,8 +1,3 @@
-# Placeholder until Story 6.5 ships tests/mainnet_smoke.rs and the
-# mainnet-smoke cargo feature. The job is fully gated on the existence of
-# `tests/mainnet_smoke.rs` so the cron stays a no-op until then — without
-# the guard, the cron would be permanently red on Day 1 because the feature
-# and the test file do not yet exist.
 name: Nightly Mainnet Smoke
 
 on:
@@ -38,24 +33,19 @@ jobs:
     # level forces job status to success and silently kills the notification
     # path.
     #
-    # Soft-gate: this workflow is a no-op until Story 6.5 ships the test file
-    # AND the `mainnet-smoke` cargo feature. Without this guard,
-    # `cargo test --features mainnet-smoke` would error out with
-    # "feature `mainnet-smoke` does not exist" and the cron would be red.
-    if: hashFiles('tests/mainnet_smoke.rs') != ''
+    # The `Verify mainnet-smoke cargo feature exists` step below gates all
+    # subsequent steps — if the cargo feature is absent it short-circuits
+    # cleanly without failing the workflow.
     steps:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 1
       - name: Verify mainnet-smoke cargo feature exists
         id: feature_check
-        # Belt-and-braces guard alongside the job-level `hashFiles` check —
         # `tests/mainnet_smoke.rs` and `[features] mainnet-smoke = []` may
-        # land in separate PRs, and the cargo feature must exist before
-        # `cargo test --features mainnet-smoke` is run. We set an output
-        # rather than failing the step so the rest of the job can short-
-        # circuit cleanly via `if:` (GitHub Actions has no native "skip"
-        # exit code).
+        # land in separate PRs. We set an output rather than failing the step
+        # so the rest of the job can short-circuit cleanly via `if:` (GitHub
+        # Actions has no native "skip" exit code).
         run: |
           if grep -q '^mainnet-smoke\b' Cargo.toml; then
             echo "feature_present=true" >> "$GITHUB_OUTPUT"