fix(plugins): stamp surface identity at record time, not send time

Six defects in 0.3.x plugin telemetry. Defects 1, 2 and 6 were not three bugs:
they were one spool protocol getting three properties wrong.

Identity was decided by the wrong process. `harness` was stamped in record(),
correctly, but `source` was read from a module global in flush() — so whichever
process drained the spool named every event in it. Two processes never call
init(): mcp_server.py, and the detached `python3 telemetry.py` sender that
spawn_flush() starts. record() now stamps source beside harness, and the build
generates core/_harness_id.py per host so identity resolves with no init() call
at all. That also unifies two defaults that disagreed (`<host>_plugin` vs
`MEM0_<HOST>_PLUGIN`), which could yield three source values for one plugin.

Ownership was inferred, not held. Path.replace is os.rename, which preserves
mtime, so a claim made after a quiet minute inherited the spool's age and was
stealable the instant it existed. Claims are touched on creation and the
per-batch rewrite doubles as a lease heartbeat.

Progress was not durable. flush() returned on the first failed batch without
truncating, so the retry re-posted from index 0 — 150 events delivered 250
times. It now rewrites the claim with the unsent remainder after every batch,
bounding a crash to one repeated batch, and each event carries a uuid.

Parked batches starved. They were only reachable when no spool existed, and
because sessions keep recording there usually was one, so a batch parked by a
failed send waited until the 7-day expiry deleted it unsent — despite its own
presence being what starts the sender. flush() drains them in the same run, and
expiry now applies only after a genuine retry has failed.

code.install counted upgrades and repeat sessions. is_first_run() read the
identity file, which only a successful flush writes, so an offline user recorded
an install every session forever. A dedicated install-state.json is claimed
atomically at record time; a non-empty data directory reads as an upgrade.

The docs called this anonymous. Every event carries the account email, and the
hashes were unsalted SHA-256 over a git remote URL or an absolute path
containing the username. READMEs, the module docstring and a new docs section
now say what the code does, and repo/session digests are salted per install.

A cached email outlived an API key change. It is now re-resolved when the key's
fingerprint differs, and $identify aliases anonymous->email only — aliasing one
account to another merges person profiles irreversibly.

All six shipped green because the shared core's only tests lived under one host,
behind a conftest that calls init() at import. Core behaviour was never
exercised uninitialised. Adds agent-plugin-core/tests with no init, including
subprocess tests and coverage for the portable plugin, which has no flush worker
and would pass a native-only test vacuously.

Also puts the three surface headers on the SDKs, CLIs and integrations, and
corrects a README claiming ZAPIER/STRANDS were already in the platform allowlist.

Verified: 59 core tests, 203 claude-code, 11 cursor, 5 codex, 2 kimi, 6
antigravity. ruff and compileall clean. --check clean for all six hosts.
TypeScript changes are not typechecked locally (deps not installed).

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`.