docs: scope AGENTS instructions by directory (#2083)

crates/ecstore/AGENTS.md

@@ -0,0 +1,28 @@
+# ECStore Crate Instructions
+
+Applies to `crates/ecstore/`.
+
+## Data Durability and Integrity
+
+- Do not weaken quorum checks, bitrot checks, or metadata validation paths.
+- Treat any change affecting read/write/repair correctness as high risk and test accordingly.
+- Prefer explicit failure over silent data corruption or implicit success.
+
+## Performance-Critical Paths
+
+- Be careful with allocations and locking in hot paths.
+- Keep network and disk operations async-friendly; avoid introducing unnecessary blocking.
+- Benchmark-sensitive changes should include measurable rationale.
+
+## Cross-Module Coordination
+
+- Validate behavior impacts on:
+  - `rustfs/src/storage/`
+  - `crates/filemeta/`
+  - `crates/heal/`
+  - `crates/checksums/`
+
+## Suggested Validation
+
+- `cargo test -p rustfs-ecstore`
+- Full gate before commit: `make pre-commit`