Resolve Client.Python-003, -005, -009 code-review findings

Client.Python-003: stream_events_raw and query_active_alarms passed `timeout`
to the stub with no TypeError fallback, unlike _unary. Both now route through
a shared _open_stream helper that strips `timeout` on TypeError.

Client.Python-005: discover_hierarchy buffered the entire Galaxy hierarchy in
memory. Added GalaxyRepositoryClient.iter_hierarchy, a lazy async generator
yielding objects page-by-page; discover_hierarchy is now a thin wrapper that
preserves its list contract. README documents iter_hierarchy.

Client.Python-009: added regression coverage for previously untested paths —
write2/add_item2 request shape, the MAX_BULK_ITEMS boundary, the None-argument
TypeError guards, TLS ca_file reading, and the non-auth map_rpc_error fallthrough.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

code-reviews/Client.Python/findings.md

@@ -7,7 +7,7 @@
 | Review date | 2026-05-18 |
 | Commit reviewed | `3cc53a8` |
 | Status | Reviewed |
-| Open findings | 12 |
+| Open findings | 9 |
 
 ## Checklist coverage
 
@@ -63,13 +63,13 @@
 | Severity | Medium |
 | Category | Error handling & resilience |
 | Location | `clients/python/src/mxgateway/client.py:125-137,155-173` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `stream_events_raw` and `query_active_alarms` call the stub directly with a `timeout` kwarg when `stream_timeout` is set, with no `TypeError` fallback. `galaxy.py:watch_deploy_events` and `_unary` *do* have a fallback that strips `timeout` if the callable rejects it. This asymmetry means a fake/older stub that does not accept `timeout` crashes for gateway streams but not Galaxy streams. It is only masked today because `stream_timeout` defaults to `None`.
 
 **Recommendation:** Apply the same `try/except TypeError` timeout-fallback pattern to `stream_events_raw` and `query_active_alarms`, or remove the fallback everywhere and standardise on a single behaviour.
 
-**Resolution:** _(open)_
+**Resolution:** 2026-05-18 — Confirmed: both stream methods in `client.py` called the stub with `timeout` unconditionally and had no `TypeError` fallback, unlike `_unary` and `galaxy.watch_deploy_events`. Added a shared `_open_stream` helper in `client.py` that opens a server-streaming call and strips the `timeout` kwarg when the stub raises `TypeError: ... unexpected keyword argument 'timeout'`, then routed both `stream_events_raw` and `query_active_alarms` through it. Regression tests in `tests/test_stream_timeout_fallback.py` (`test_stream_events_raw_falls_back_when_stub_rejects_timeout`, `test_query_active_alarms_falls_back_when_stub_rejects_timeout`, `test_stream_events_raw_still_passes_timeout_to_capable_stub`) failed before the fix and pass after. No public behaviour change for real gRPC stubs, so no README update needed.
 
 ### Client.Python-004
 
@@ -93,13 +93,13 @@
 | Severity | Medium |
 | Category | Performance & resource management |
 | Location | `clients/python/src/mxgateway/galaxy.py:117-140` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `discover_hierarchy` pages through the entire Galaxy object hierarchy and accumulates every `GalaxyObject` (each carrying its full attribute list) into a single in-memory `list` before returning. For a large Galaxy this is a very large allocation with no streaming alternative and no caller-side bound.
 
 **Recommendation:** Offer an async-generator variant (e.g. `iter_hierarchy()`) that yields objects/pages as they arrive, keeping `discover_hierarchy()` as a convenience wrapper. At minimum document the memory characteristic.
 
-**Resolution:** _(open)_
+**Resolution:** 2026-05-18 — Confirmed: `discover_hierarchy` buffered the entire hierarchy with no streaming alternative. Added `GalaxyRepositoryClient.iter_hierarchy`, an async generator that fetches one `DiscoverHierarchyRequest` page at a time and yields each `GalaxyObject` as it arrives, so peak memory is bounded by a single page (`_DISCOVER_HIERARCHY_PAGE_SIZE`). Pages are fetched lazily — the next page is only requested after the current page is fully consumed. `discover_hierarchy` is now a thin convenience wrapper (`[obj async for obj in self.iter_hierarchy()]`) that preserves its `list[GalaxyObject]` contract, including the repeated-page-token guard. Regression tests in `tests/test_galaxy_iter_hierarchy.py` (`test_iter_hierarchy_yields_objects_across_pages`, `test_iter_hierarchy_is_lazy_and_does_not_prefetch_next_page`, `test_iter_hierarchy_rejects_repeated_page_token`, `test_discover_hierarchy_still_returns_full_list`) failed before the fix and pass after. `clients/python/README.md` updated with the `iter_hierarchy` usage and memory guidance since this adds a new public method.
 
 ### Client.Python-006
 
@@ -153,13 +153,13 @@
 | Severity | Medium |
 | Category | Testing coverage |
 | Location | `clients/python/tests/` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** Several non-trivial public paths are untested: `Session.write2`/`add_item2` request construction; the bulk-size limit `_ensure_bulk_size`/`MAX_BULK_ITEMS` guard; the `None`-argument `TypeError` guards in bulk methods; the TLS `ca_file` read path in `create_channel`; most CLI command bodies; and `map_rpc_error`'s default (non-auth) branch.
 
 **Recommendation:** Add tests for `write2`/`add_item2` request shape, the bulk-size `ValueError`, the `ca_file` TLS branch, the generic `map_rpc_error` fallthrough, and at least one happy-path CLI command using a fake stub.
 
-**Resolution:** _(open)_
+**Resolution:** 2026-05-18 — Confirmed coverage gap against the existing `tests/` files. Added `tests/test_coverage_gaps.py` covering every path the finding lists: `test_add_item2_sends_item_context_and_returns_handle` and `test_write2_sends_value_and_timestamp_value` (request shape + `MxValue` oneof), `test_subscribe_bulk_rejects_oversized_request` and `test_add_item_bulk_at_limit_is_allowed` (the `MAX_BULK_ITEMS` `_ensure_bulk_size` boundary), `test_advise_item_bulk_rejects_none_argument` (the `None`-argument `TypeError` guard), `test_create_channel_reads_ca_file` and `test_create_channel_missing_ca_file_raises` (the TLS `ca_file` read path), `test_map_rpc_error_generic_branch_returns_transport_error` and `test_map_rpc_error_handles_error_without_code` (the non-auth `map_rpc_error` fallthrough and the no-`code` path), and `test_cli_register_happy_path_emits_server_handle` (a happy-path CLI command body driven end to end through `CliRunner` with a fake stub via a monkeypatched `_connect`). All 10 new tests pass. No source change required — this is a pure coverage finding.
 
 ### Client.Python-010