feat(integrations): declare which surface each client is, and its version

Nothing on the wire said which Mem0 surface made a call. Both SDKs sent only an
auth header, so the platform saw python-httpx and axios and attributed every
plugin, wrapper and direct API user to one undifferentiated bucket. Version was
unknowable, which is what gates every deprecation decision.

Three headers, and the rules on them are the point:

- X-Mem0-Source and X-Application are SET-ONCE. Whichever layer is outermost
  sets them; nothing below overwrites. A plugin wrapping the SDK keeps its own
  identity instead of being renamed by the transport underneath it.
- X-Mem0-Client is APPEND-ONLY. A plugin calling the Python SDK produces
  `mem0-plugin/0.3.1, mem0-python/2.0.19`, so neither layer can erase the other.

Deliberately not User-Agent: proxies rewrite it, and we have already met a WAF
that 403s on it.

The plugin core also hoists `source` out of metadata to the top level, which is
where the backend actually reads it. It sat in metadata, which get_event_source
never consults, so all six plugins arrived indistinguishable from a raw SDK call
no matter what they set. The harness tag stays in metadata as hook provenance.

pi-agent had PI_AGENT as a PostHog property only and never sent it on the wire.
vercel-ai-sdk sent nothing at all from its raw fetch calls.

Values must exist in the platform's EventSource enum or they bucket to OTHERS,
so integrations/AGENTS.md now states the contract and the "adding an
integration" checklist requires landing the platform value in the same week.

Pairs with mem0ai/platform#3602, which recognizes these values.

TypeScript changes are not typechecked locally — deps are not installed for
those packages. CI covers them.

Claude-Session: https://claude.ai/code/session_01C7tEmH86HAr7GoAAKCEHZb

integrations/AGENTS.md

@@ -49,6 +49,29 @@ Run the type check after every TypeScript change: `pnpm run typecheck` or `tsc -
 - **`zapier-mem0/`** is a Zapier Platform CLI app: add, search, get, delete. It deploys to Zapier, not npm, so it is **not** in the release router. Deploy it with `gh workflow run zapier-mem0-cd.yml --ref main` (needs the `ZAPIER_DEPLOY_KEY` secret).
 - **`mem0-strands/`** is a native Strands `MemoryStore` (Python, published to PyPI as `mem0-strands`). It plugs into the Strands `MemoryManager` for automatic recall and server-side extraction, over the hosted Mem0 platform or self-hosted Mem0 OSS. The package lives under `mem0-strands/python/`.
 
+## Surface attribution
+
+Every integration tells the Mem0 platform which surface it is. Three headers,
+and the rules on them are what keep one layer from erasing another:
+
+| Header | Carries | Rule |
+|--------|---------|------|
+| `X-Mem0-Source` | one canonical source value | **set-once** — write only if absent |
+| `X-Application` | the host app it runs inside | **set-once** — write only if absent |
+| `X-Mem0-Client` | `name/version`, outermost first | **append-only** — add yourself, never replace |
+
+Set-once means `setdefault`, never assignment. An integration that wraps the
+SDK is the outermost layer and sets the source; the SDK underneath must defer to
+it. Assignment is exactly how every agent plugin came to be indistinguishable
+from every other one at the platform.
+
+Append-only means a plugin calling the Python SDK produces
+`mem0-plugin/0.3.1, mem0-python/2.0.19`, so neither layer can erase the other.
+
+The backend recognizes a fixed list of source values and buckets everything else
+into `OTHERS`. A new value has to land in the platform's `EventSource` enum, so
+do not invent one without that change going in too.
+
 ## Adding an integration
 
 1. For a native coding-agent host, add `integrations/<name>-plugin/` with `plugin-build.json`, its manifest, and a thin adapter, then generate its shared runtime. Portable clients use the single `mem0-agent-plugin/` package. Independent TypeScript integrations stay self-contained and import shared lifecycle behavior from `agent-plugin-core/typescript/`.
@@ -59,3 +82,4 @@ Run the type check after every TypeScript change: `pnpm run typecheck` or `tsc -
 5. If it is a Claude Code or editor marketplace plugin, register the generated native bundle path in the applicable marketplace files. Preserve the existing public plugin name.
 6. Document it under `docs/integrations/` and add the page to `docs/docs.json` and `docs/llms.txt`.
 7. Add rows to the table above and to the CI/CD tables in [`../.github/AGENTS.md`](../.github/AGENTS.md).
+8. Send the three headers in [Surface attribution](#surface-attribution), and land the matching `EventSource` value on the platform in the same week. Until it exists, your traffic reports as `OTHERS`.