copilot: address PR feedback

- checkout@v5 -> @v6 to match rest of repo
- Pin cargo-nextest to 0.9.101 (matches cfg_versions.rs) instead of 'latest'
- Rephrase inner loop description: covers common early CI failures,
  not 'the same errors as CI job0'

Author: jstarks

.github/copilot-instructions.md

@@ -121,8 +121,9 @@ This project uses the **Rust 2024 edition** (`edition = "2024"` in root
 ## Autonomous Agent Inner Loop
 
 When running as a coding agent (GitHub Copilot coding agent or similar),
-follow this validation loop **before pushing each commit**. This catches
-the same errors as CI job0 locally, avoiding slow push-and-wait cycles.
+follow this validation loop **before pushing each commit**. This covers
+the common early CI failures (including the fmt + clippy checks from job0)
+locally, avoiding slow push-and-wait cycles.
 
 1. **Identify modified packages.** For each file you changed, find the
    crate's `Cargo.toml` and note the package name.

.github/workflows/copilot-setup-steps.yml

@@ -18,7 +18,7 @@ jobs:
       contents: read
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Install the exact Rust toolchain used by CI.
       - name: Install Rust toolchain
@@ -28,9 +28,11 @@ jobs:
           echo "$HOME/.cargo/bin" >> "$GITHUB_PATH"
 
       # Install cargo-nextest so the agent can run unit tests.
+      # Keep this version in sync with NEXTEST in
+      # flowey/flowey_lib_hvlite/src/_jobs/cfg_versions.rs
       - name: Install cargo-nextest
         run: |
-          curl -LsSf https://get.nexte.st/latest/linux | tar zxf - -C "$HOME/.cargo/bin"
+          curl -LsSf https://get.nexte.st/0.9.101/linux | tar zxf - -C "$HOME/.cargo/bin"
 
       # Restore protoc and other build dependencies via the canonical
       # flowey pipeline. This compiles flowey_hvlite first, then downloads