diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
index 72ed6387e1a..92e09afb98e 100644
--- a/.github/copilot-instructions.md
+++ b/.github/copilot-instructions.md
@@ -74,7 +74,11 @@ void function() {
 - Classes: `CamelCase` → `HttpSM`, `NetVConnection`, `CacheProcessor`
 - Functions/variables: `snake_case` → `handle_request()`, `server_port`, `cache_key`
 - Constants/macros: `UPPER_CASE` → `HTTP_STATUS_OK`, `MAX_BUFFER_SIZE`
-- Member variables: `snake_case` with no prefix → `connection_count`, `buffer_size`
+- Private member variables use both `_` and `m_` prefixes in the source code;
+  be consistent with the surrounding code. For new files, prefer the `_` prefix
+  because that reflects the community consensus.
+- Boolean variables and functions returning boolean values are named as
+  predicates: use `was_modified` rather than `modified`.
 
 **C++20 Patterns (Use These):**
 ```cpp
@@ -153,6 +157,7 @@ for (auto &conn : connections) {
 - Python 3.11+ with type hints
 - 4-space indentation (never tabs)
 - Type annotations on all function signatures
+- Use f'...' strings rather than .format() strings for new Python code.
 
 ### License Headers
 
@@ -358,7 +363,9 @@ plugins/my_plugin/
 **When adding new functionality:**
 1. Check if unit tests exist in same directory (Catch2)
 2. Add integration tests in `tests/gold_tests/` (autest)
-3. Prefer `Test.ATSReplayTest()` with `replay.yaml` format (Proxy Verifier)
+3. Prefer `Test.ATSReplayTest()` with `replay.yaml` format (Proxy Verifier). If
+   `ATSReplayTest` doesn't fit, prefer organizing the test around a test class with
+   separate functions for configuring the servers, ATS, client, etc.
 4. Test both success and error paths
 
 ## Configuration
diff --git a/AGENTS.md b/AGENTS.md
index e045c3c648f..d866f1845ff 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -123,12 +123,15 @@ regularly).
 using the Proxy Verifier format. This is simpler, more maintainable, and
 parseable by tools.
 
-**Python conventions for test and helper scripts:**
-- Launch Python helpers with `{sys.executable}` rather than a hardcoded `python3`,
-  so the test runs under the same interpreter the harness uses.
-- Prefer f-strings over `str.format()` when building command lines, config lines,
-  and `Testers` expressions.
-- Add type annotations to helper functions.
+If `ATSReplayTest` is not a good fit (say, the test needs a custom client), then
+organize the test around a test class with member functions that configure any
+servers, the ATS process, and the client. See
+`tests/gold_tests/ats_probe/ats_probe.test.py` for an example of a test organized
+around a test class.
+
+In autests, launch Python helpers with `{sys.executable}` rather than a
+hardcoded `python3`, so the test runs under the same interpreter the harness
+uses.
 
 **For complete details on writing autests, see:**
 - `doc/developer-guide/testing/autests.en.rst` - Comprehensive guide to autest
@@ -313,7 +316,11 @@ SMDebug(dbg_ctl, "Processing request for URL: %s", url);
 - CamelCase for classes: `HttpSM`, `NetVConnection`
 - snake_case for variables and functions: `server_entry`, `handle_api_return()`
 - UPPER_CASE for macros and constants: `HTTP_SM_SET_DEFAULT_HANDLER`
-- Private member variables have the `m_` prefix.
+- Private member variables use both `_` and `m_` prefixes in the source code;
+  be consistent with the surrounding code. For new files, prefer the `_` prefix
+  because that reflects the community consensus.
+- Boolean variables and functions returning boolean values are named as
+  predicates: use `was_modified` rather than `modified`.
 
 **Doxygen Comments:**
 
@@ -364,6 +371,9 @@ MIOBuffer *buffer = (MIOBuffer*)malloc(sizeof(MIOBuffer));
 ### Python Code Style (for tests and tools)
 - Python 3.11+ with proper type annotations
 - 4-space indentation, never TABs
+- Type annotations on all function signatures
+- Prefer f-strings over `str.format()` when building command lines, config lines,
+  and `Testers` expressions.
 
 ### Memory Management
 - Custom allocators supported (jemalloc, mimalloc)