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/pi-agent-plugin/src/commands.ts

@@ -22,6 +22,10 @@ export function registerCommands(
   const pluralize = (n: number, one: string, many: string): string =>
     `${n} ${n === 1 ? one : many}`;
 
+// Surface attribution on the wire. This was previously only a PostHog property,
+// so the platform saw these calls as generic SDK traffic.
+const PLATFORM_SOURCE = "PI_AGENT";
+
   const searchMemories = async (query: string, scope: Scope) => {
     const filters = resolveSearchFilters(scope, getScopeCtx());
     const result = await mem0.search(query, {
@@ -29,7 +33,8 @@ export function registerCommands(
       threshold: config.searchThreshold,
       topK: SEARCH_TOP_K,
       rerank: true,
-    });
+      source: PLATFORM_SOURCE,
+    } as never);
     return result.results ?? [];
   };
 
@@ -45,7 +50,7 @@ export function registerCommands(
       const addParams = resolveAddParams(config.defaultScope, getScopeCtx());
       const result = await mem0.add(
         [{ role: "user", content: text }],
-        { ...addParams, customCategories: DEFAULT_CUSTOM_CATEGORIES, infer: false },
+        { ...addParams, customCategories: DEFAULT_CUSTOM_CATEGORIES, infer: false, source: PLATFORM_SOURCE } as never,
       );
       captureCommandEvent("mem0-remember", {}, telemetryCtx);