fix(gateway): preserve thread routing from cached live session sources

[teknium1]

Salvage of #20325 (@Zyproth) onto current main + LRU cap follow-up.

Summary

Threaded/group sessions were losing thread_id in two gateway fallback routing paths (shutdown notifications, synthetic background-process events) when persisted SessionEntry.origin was missing. _parse_session_key deliberately drops thread_id for group/channel keys because the 6th segment is ambiguous (thread_id vs user_id depending on isolation mode). The fix caches the live SessionSource in-memory and consults that cache before falling back to key parsing.

Commits

1. 07517da — Zyproth's original fix (authorship preserved)
2. e7bba82 — follow-up: cap _session_sources at 512 entries with OrderedDict LRU eviction so long-running gateways can't accumulate stale entries forever

Validation

• 53 targeted gateway tests pass (test_background_process_notifications.py + test_restart_notification.py)
• Full tests/gateway/ sweep: 4679/4680 pass; the one failure (test_discord_free_channel_skips_auto_thread) is pre-existing on clean main, unrelated

Closes #20325

[github-actions]

🔎 Lint report: hermes/hermes-651549e0 vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 7485 on HEAD, 7467 on base (🆕 +18)

🆕 New issues (16):

Rule	Count
invalid-argument-type	8
unresolved-attribute	4
unsupported-operator	3
not-subscriptable	1

First entries

tests/run_agent/test_provider_attribution_headers.py:130: [unsupported-operator] unsupported-operator: Operator `not in` is not supported between objects of type `Literal["X-OpenRouter-Cache"]` and `Unknown | str | dict[str, str] | ... omitted 3 union elements`
tests/run_agent/test_provider_attribution_headers.py:129: [not-subscriptable] not-subscriptable: Cannot subscript object of type `int` with no `__getitem__` method
run_agent.py:2437: [invalid-argument-type] invalid-argument-type: Argument to function `get_model_context_length` is incorrect: Expected `str`, found `str | dict[str, str] | Any | ... omitted 3 union elements`
tests/agent/test_codex_cloudflare_headers.py:181: [unsupported-operator] unsupported-operator: Operator `in` is not supported between objects of type `Literal["originator"]` and `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 3 union elements`
tests/run_agent/test_provider_attribution_headers.py:131: [unsupported-operator] unsupported-operator: Operator `not in` is not supported between objects of type `Literal["X-OpenRouter-Cache-TTL"]` and `Unknown | str | dict[str, str] | ... omitted 3 union elements`
run_agent.py:12318: [invalid-argument-type] invalid-argument-type: Argument to function `len` is incorrect: Expected `Sized`, found `(str & ~AlwaysFalsy) | (dict[Unknown, Unknown] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 3 union elements`
run_agent.py:2160: [invalid-argument-type] invalid-argument-type: Argument to function `query_ollama_num_ctx` is incorrect: Expected `str`, found `(str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 4 union elements`
run_agent.py:6454: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 3 union elements`
run_agent.py:6283: [invalid-argument-type] invalid-argument-type: Argument to function `_codex_cloudflare_headers` is incorrect: Expected `str`, found `Unknown | str | dict[str, str] | ... omitted 3 union elements`
tests/run_agent/test_provider_attribution_headers.py:65: [unresolved-attribute] unresolved-attribute: Attribute `startswith` is not defined on `dict[str, str]` in union `Unknown | str | dict[str, str]`
tests/gateway/test_restart_notification.py:621: [unresolved-attribute] unresolved-attribute: Object of type `bound method BasePlatformAdapter.send(chat_id: str, content: str, reply_to: str | None = None, metadata: dict[str, Any] | None = None) -> CoroutineType[Any, Any, SendResult]` has no attribute `assert_awaited_once_with`
run_agent.py:2389: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 4 union elements`
tests/agent/test_codex_cloudflare_headers.py:163: [unresolved-attribute] unresolved-attribute: Attribute `get` is not defined on `str & ~AlwaysFalsy`, `int & ~AlwaysFalsy` in union `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 3 union elements`
run_agent.py:2386: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 4 union elements`
run_agent.py:12315: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 3 union elements`
tests/agent/test_codex_cloudflare_headers.py:163: [unresolved-attribute] unresolved-attribute: Attribute `startswith` is not defined on `dict[str, str]` in union `Unknown | str | dict[str, str]`

✅ Fixed issues (9):

Rule	Count
invalid-argument-type	8
unresolved-attribute	1

First entries

tests/agent/test_codex_cloudflare_headers.py:163: [unresolved-attribute] unresolved-attribute: Attribute `get` is not defined on `str & ~AlwaysFalsy` in union `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | dict[Unknown, Unknown] | Divergent`
run_agent.py:2437: [invalid-argument-type] invalid-argument-type: Argument to function `get_model_context_length` is incorrect: Expected `str`, found `str | dict[str, str] | Any | ... omitted 4 union elements`
run_agent.py:12318: [invalid-argument-type] invalid-argument-type: Argument to function `len` is incorrect: Expected `Sized`, found `(str & ~AlwaysFalsy) | (dict[Unknown, Unknown] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 4 union elements`
run_agent.py:6454: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 4 union elements`
run_agent.py:12315: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `str | dict[Unknown, Unknown] | Any | ... omitted 4 union elements`
run_agent.py:2160: [invalid-argument-type] invalid-argument-type: Argument to function `query_ollama_num_ctx` is incorrect: Expected `str`, found `(str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | (Any & ~AlwaysFalsy) | ... omitted 5 union elements`
run_agent.py:2389: [invalid-argument-type] invalid-argument-type: Argument to function `_is_oauth_token` is incorrect: Expected `str`, found `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 5 union elements`
run_agent.py:2386: [invalid-argument-type] invalid-argument-type: Argument to function `build_anthropic_client` is incorrect: Expected `str`, found `(Unknown & ~AlwaysFalsy) | (str & ~AlwaysFalsy) | (dict[str, str] & ~AlwaysFalsy) | ... omitted 5 union elements`
run_agent.py:6283: [invalid-argument-type] invalid-argument-type: Argument to function `_codex_cloudflare_headers` is incorrect: Expected `str`, found `Unknown | str | dict[str, str] | dict[Unknown, Unknown] | Divergent`

Unchanged: 3917 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.