add AGENTS.md and CLAUDE.md

Cross-vendor agent doc with the project-specific bits not derivable
from README or code: test filter env vars, the leak-detection test
invariant, the exact zig fmt CI command, and a pointer to mirror
neighboring file conventions for @import alias case and struct-init
inference. CLAUDE.md is a one-line @AGENTS.md import shim for Claude
Code, which doesn't read AGENTS.md natively.

AGENTS.md

@@ -0,0 +1,29 @@
+# AGENTS.md
+
+## Tests
+
+```bash
+make test                                       # Run all tests
+make test F="server"                            # Filter by substring
+TEST_FILTER="WebApi: #selector_all" make test   # Filter main + subtest (separator: #)
+TEST_VERBOSE=true make test
+TEST_FAIL_FIRST=true make test
+METRICS=true make test                          # Capture allocation/duration metrics as JSON
+```
+
+The custom test runner (`src/test_runner.zig`) detects memory leaks in debug builds. **A test that allocates without freeing fails** — not just lints.
+
+## Formatting
+
+```bash
+zig fmt --check ./*.zig ./**/*.zig    # Exact command CI runs
+```
+
+`zig build` depends on the fmt step, so a local build catches drift too.
+
+## Conventions
+
+Mirror the patterns in neighboring files. In particular:
+
+- `@import` alias case follows the imported file's basename (`const Frame = @import("Frame.zig")`, `const ast = @import("ast.zig")`).
+- Prefer struct-init type inference (`.{ ... }`) where the expected type is known from the function signature or variable annotation.

CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md