test(telemetry): cover the pipeline and the backend contract

[pblazej]

Summary

Tests for #1483: the pipeline end to end, and the backend contract one test per row. Every link below points at the stage that adds the test.

Changes

• telemetry.rs: the pipeline end to end through a scripted transport
• backend_tests.rs: the backend contract, one test per row, including a mock collector over the real livekit-net HTTP stack
• The one telemetry.rs test that needs global arrives with it in feat(telemetry): add the process-wide pipeline and opt-out #1485

Backend contract: every status code and condition → behaviour → test (29 rows)

A Room hands over its server URL and token; only a parsed *.livekit.cloud host over TLS gets https://<host>/observability/client/{logs,traces}/otlp/v0 with Authorization: Bearer <token>. Every collector answer is classified by the core; behaviour marked custom is not prescribed by the OTLP/HTTP spec.

Condition	Behaviour	Test	Why
Server URL	parsed (WHATWG); token only for a TLS scheme, a domain under .livekit.cloud with its own label, default port, no userinfo; endpoint built from that host alone; anything else collects nothing	look_alike_server_urls_never_get_the_token only_livekit_cloud_hosts_get_an_ingest_url the_ingest_url_and_token_come_from_the_room self_hosted_servers_get_nothing_and_nothing_is_kept	custom — self-hosted servers have no ingest (CLT-3335); credentials only to the authorized origin
Token handed over again	same pair: no-op (a reconnect retries a 404'd ingest); new token: uploads resume at once	handing_over_the_same_token_again_is_free a_reconnect_with_the_same_token_retries_a_404 an_expired_token_holds_uploads_until_a_fresh_one_arrives	RFC 6750 bearer; custom refresh contract
Token expired or missing	never sent; batches wait (hard hold). A past, negative, fractional-past or non-numeric exp is expired; only a missing one means no known expiry; a far-future one is clamped to a year	an_expired_token_holds_uploads_until_a_fresh_one_arrives untrusted_expiry_claims_fail_closed uploads_wait_for_a_destination hard_holds_have_no_escape_hatch	custom — untrusted claims fail closed
First token lacks the observability grant	nothing collected for that project	a_room_without_the_observability_grant_sends_nothing a_token_without_the_grant_is_not_consent	custom — the grant is the customer's consent
Refresh drops the grant (today's SFU)	keep the granted token until it expires, then wait	a_refresh_that_drops_the_grant_keeps_uploading_with_the_granted_token a_refresh_that_drops_the_grant_keeps_the_granted_token_until_it_expires	custom — bridge until OCD-3387
Ownership	each record (and each RTC window, at open) captures (project, session); credentials keyed by it; the answer is attributed to the project the request went to; a Room switching projects takes nothing along; an unconnected Room never borrows another Room's project; a Room's records from before it connected, cached ones included, are bound on disk to that Room's first project by the exporter pass its connect wakes (at once if the exporter is idle, otherwise once the export pass then running finishes; no single-request bound), so they replay after a restart; a crash once a batch's bound copy is journaled rolls forward to it. A Room that never connects before the process ends — or a process killed after the connect but before that batch's bound copy is journaled — leaves the batch unowned: held until the 24 h expiry, then counted expired	answers_to_pre_connect_batches_are_attributed_to_their_own_project pre_connect_records_replay_after_a_restart a_crash_while_binding_still_replays_to_the_rooms_project a_room_switching_projects_takes_nothing_along an_unconnected_room_never_borrows_another_rooms_project two_rooms_on_two_projects_never_share_a_token_or_a_destination ownership_survives_a_room_changing_projects rooms_never_borrow_each_others_tokens	custom — never borrow a credential (RFC 6750 §5.2)
Credential lifecycle	a refusal is recorded by credential identity, shared by every slot (Room, project copy, process route, restart), until the token expires; a session's credentials stay while it is alive (one per project it used) or cached batches need them — pre-connect batches included; project copies only while needed	refusals_stick_and_credentials_follow_live_rooms a_gone_rooms_pre_connect_backlog_keeps_its_credential	custom
Restart with cached data, no token	wait for a token of the same project (≤ 24 h); tokens never persisted	a_restart_with_cached_data_and_no_token_waits_for_the_same_project	custom
2xx	batch removed	batches_events_into_one_otlp_request	OTLP specifies 200 for success; accepting every 2xx is custom
2xx + partial_success	rejected records counted, never retried	partial_success_counts_the_refused_records_and_never_retries success_and_partial_success	OTLP: MUST NOT retry partial success
400, 3xx, other 4xx	dropped, counted rejected; a delay hint changes nothing	a_bad_request_drops_the_batch client_errors delay_hints_never_make_a_final_status_retryable	OTLP: not retryable
413	halves replace the batch in a journaled cache transaction (on disk stays on disk), retried at once down to one record, each against the pass budget; a lone oversized record dropped (oversized)	payload_too_large_splits_down_to_single_records a_split_never_moves_a_batch_off_the_disk (added in #1485) a_split_crashed_at_every_step_loses_and_duplicates_nothing	custom — OTLP only says don't retry as-is; RFC 9110 §15.5.14 (test lands in #1485)
401/403 "data recording is disabled by owner"	project silent for the process, its cache purged	disabled_project_goes_silent_and_purges_its_cache disabled_by_owner	custom — exact phrase match, no machine code yet
Other 401/403	kept; that token never sent again; wait for the next	unauthorized_holds_the_batch_until_a_new_token repeated_unauthorized_answers_wait_for_renewal_without_loss a_refused_token_is_never_sent_again	custom — RFC 9110 §15.5.2
404	project silent until its next token or a reconnect; cache purged	not_found_on_the_derived_endpoint_goes_silent not_found_recovers_with_the_next_token_disabled_does_not a_reconnect_with_the_same_token_retries_a_404	custom (CLT-3335), scoped to the origin
429	that destination pauses for Retry-After, else RetryInfo, else 60 s; collection continues	throttling_honors_retry_after_then_retry_info_then_a_minute a_real_http_collector_throttles_and_recovers	OTLP: retryable, honor Retry-After; RFC 6585 §4; 60 s default custom
503 with a delay	that destination pauses for it	throttling_honors_retry_after_then_retry_info_then_a_minute	OTLP: retryable; RFC 9110 §10.2.3
502 / 503 / 504	backoff 1 s → 60 s, full jitter; exhaustion pauses, never deletes (24 h retention)	a_failing_server_never_costs_a_batch server_errors	OTLP: retryable with exponential backoff; the constants and retention are custom
500 + RetryInfo	retried after the named delay (a header alone does not count)	a_retryable_500_waits_for_its_retry_info delay_hints_never_make_a_final_status_retryable	custom — Cloud sends retryable 500s
Other 5xx	dropped, counted rejected	other_server_errors_drop_the_batch	OTLP: MUST NOT retry
Retry-After / RetryInfo values	seconds or HTTP-date; garbage ignored, negative → now, oversized saturates; clamped to 24 h; shutdown never cuts it short	untrusted_time_values_are_bounded retry_after_http_dates shutdown_never_cuts_a_server_delay_short	RFC 9110 §10.2.3; the clamp is custom
One project failing	only that destination pauses; evictions count as throttled only for the paused destination	a_failing_project_does_not_pause_the_others	custom
Timeout	backoff; counted apart	timeouts_are_counted_apart_from_failures	OTLP: retryable
Connection, DNS, TLS failure	backoff 1 s → 60 s full jitter; never a capability decision	no_answer_backs_off_exponentially_with_full_jitter backoff_doubles_with_full_jitter_up_to_a_minute	OTLP: retry with backoff
Foreign transport throws an undeclared exception	a retryable failure, not a panic (the Rust conversion hook is tested; no generated Swift/Kotlin transport test)	an_undeclared_foreign_exception_is_a_retryable_failure	custom policy on the UniFFI callback contract
Invalid request (transport-side)	dropped	an_invalid_request_is_dropped	custom — treated as permanent
Redirect	a returned 3xx drops the batch; the livekit-net client strips Authorization when the host or port changes (a scheme-only change on the same explicit port is not tested)	redirects_to_another_host_or_port_never_carry_the_token client_errors	RFC 9110 §15.4; custom
Request shape	protobuf, gzip, Priority: u=7; ≤ 512 records and ≤ 1 MiB encoded, session attributes and the self-report included; the self-report is added at most once per pass and never takes the place of real records, even at a batch size of 1; a single record over the limit dropped (oversized)	a_failing_self_report_never_starves_real_records (added in #1485) requests_are_gzipped_and_low_priority encoded_requests_stay_under_the_byte_limit_for_both_signals (added in #1485) final_limits_hold_after_decoration_and_caller_strings_are_bounded (added in #1485)	OTLP/HTTP binary + gzip; RFC 9218; the limits and the priority are custom (test lands in #1485)
Local collector	LK_TELEMETRY_ENDPOINT: everything there, no Cloud rules, no token	the_override_reaches_a_local_collector_without_cloud_rules the_override_takes_everything_without_a_token	custom, test-only, no platform API

Verification

At 3205dd2a, from a clean checkout (CI's test workflow runs only for PRs into main, so these were run locally; there is no clippy job in CI):

• cargo fmt -- --check
• cargo clippy -p livekit-telemetry --all-targets --all-features -- -D warnings
• cargo check -p livekit-telemetry --all-targets --no-default-features with features [], [net], [uniffi], [net,uniffi]
• cargo test -p livekit-telemetry: 126 unit, 2 doc; --all-features: 129 unit, 2 doc

cargo doc -D warnings reports exactly what it reports on 6aba1b68 (private-item links, ExportError::from_response).

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