diff --git a/AGENTS.md b/AGENTS.md
index 6f2e7edf..c0f30483 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -86,6 +86,32 @@ When the user requests a durable behavior change, record it here or in the relev
 ## Git Commit Conventions
 
 - Never add "Co-Authored-By" lines or any AI-attribution footers to commit messages.
+- When an agent constructs and executes the `git commit` command itself (staging, composing the message, and committing), it must append one `Assisted-by` trailer as the last line of the commit body. If the user commits manually, no trailer is required.
+- Trailer format (single line, semicolon-separated key=value):
+  `Assisted-by: harness=<harness>; primary-model=<model-id>; api-location=<domain|localhost|localnet|unknown>`
+  Examples:
+  `Assisted-by: harness=opencode; primary-model=openrouter/z-ai/glm-5.2; api-location=openrouter.ai`
+  `Assisted-by: harness=opencode; primary-model=lmstudio/qwen3-coder-next; api-location=localnet`
+- `harness`: derived from the agent identity / system prompt. Values: `opencode`, `claude`, `pi`, `hermes`, `codex`, or `unknown`.
+- `primary-model`: the exact model ID string from the system prompt (e.g. `openrouter/z-ai/glm-5.2`). No transformation.
+- `api-location`: best-effort, derived in this order:
+  1. If the provider prefix (segment before `/` in the model ID) is in the table below, use the listed domain.
+  2. Else if the provider is a known local-LLM provider (`lmstudio`, `ollama`, `llamacpp`, `vllm`, `koboldcpp`, `llama.cpp`), attempt to read the harness config for the `baseURL`: RFC1918 address → `localnet`; `127.0.0.1` or `localhost` → `localhost`; otherwise the hostname from the URL.
+  3. Else → `unknown`.
+  Known public provider table:
+  | Provider prefix | api-location |
+  |---|---|
+  | `openrouter` | `openrouter.ai` |
+  | `anthropic` | `anthropic.com` |
+  | `openai` | `openai.com` |
+  | `google` | `googleapis.com` |
+  | `mistral` | `mistral.ai` |
+  | `groq` | `groq.com` |
+  | `together` | `together.ai` |
+  | `deepseek` | `deepseek.com` |
+  | `x-ai` / `xai` | `x.ai` |
+- `secondary-models` is intentionally omitted (not reliably introspectable). May be added later if a harness surfaces subagent model info.
+- The `Assisted-by` trailer describes tooling, not authorship; it does not replace or conflict with the `Co-Authored-By` ban above.
 
 ## Child DOX Index
 
diff --git a/CLAUDE.md b/CLAUDE.md
index 00500dc8..d5f150a6 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -1,11 +1,13 @@
-# CLAUDE.md
-
-AGENTS.md is the source of truth for this repository, including for Claude harnesses.
-
-Before working, read and follow the root `AGENTS.md`, then read and follow any nested `AGENTS.md` files that apply to the paths being inspected or edited.
-
-If this file conflicts with `AGENTS.md`, `AGENTS.md` wins.
-
-## Git Commit Conventions
-
-- Never add "Co-Authored-By" lines or any AI-attribution footers to commit messages.
+# CLAUDE.md
+
+AGENTS.md is the source of truth for this repository, including for Claude harnesses.
+
+Before working, read and follow the root `AGENTS.md`, then read and follow any nested `AGENTS.md` files that apply to the paths being inspected or edited.
+
+If this file conflicts with `AGENTS.md`, `AGENTS.md` wins.
+
+## Git Commit Conventions
+
+- Never add "Co-Authored-By" lines or any AI-attribution footers to commit messages.
+- When an agent constructs and executes the `git commit` command itself (staging, composing the message, and committing), it must append one `Assisted-by` trailer as the last line of the commit body. If the user commits manually, no trailer is required.
+- Trailer format and field derivation rules live in the root `AGENTS.md` "Git Commit Conventions" section. `AGENTS.md` is the source of truth; this section is a reminder that the policy applies to Claude harnesses too.