What does this PR do?

Fixes Matrix room identity resolution so Hermes preserves explicit room names before session routing. A room with two joined members is no longer treated as a DM unless Matrix m.direct account data identifies it as direct, and explicitly named rooms keep group context even if account data is stale or conflicting.

Related Issue

No directly related issue/PR found in upstream search for Matrix room identity/session routing terms.

Type of Change

• Bug fix
• Tests

Changes Made

• gateway/platforms/matrix.py: add internal Matrix room identity resolution before DM/group routing.
• gateway/platforms/matrix.py: remove the two-member-room DM heuristic and rely on m.direct account data plus explicit room names.
• gateway/platforms/matrix.py: harden long-running adapter behavior by invalidating/reloading joined-room and DM cache state when needed, including newly joined rooms.
• tests/gateway/test_matrix_room_identity.py: add sanitized example.org regression coverage for named rooms, m.direct rooms, conflict handling, negative DM-cache reuse, empty-name fallback, dict state events, canonical aliases, non-string m.direct entries, and DM cache refresh after room joins.
• tests/gateway/test_matrix.py: update existing DM classification expectations for the corrected routing behavior.

How to Test

Latest follow-up verification after DM cache refresh hardening:

• python -m pytest tests/gateway/test_matrix_room_identity.py -q -o 'addopts=' → 12 passed
• python -m py_compile gateway/platforms/matrix.py gateway/session.py → passed
• git diff --check → passed

Earlier broader targeted run on this PR line:

• python -m pytest tests/gateway/test_matrix_room_identity.py tests/gateway/test_matrix.py -q -o 'addopts=' previously covered the combined Matrix adapter regressions. I am not re-claiming a fresh all-green full-suite run here; the latest fresh verification above is the scoped identity/cache hardening test file.

Security / Privacy Notes

• No credentials, subprocess execution, filesystem migrations, or storage schema changes.
• Tests use sanitized example.org Matrix-style fixtures only.
• Newly added runtime warning/debug logs avoid printing Matrix room IDs or room names.
• This PR intentionally does not expose expanded channel metadata; normalized channel identity is deferred to a follow-up PR.

Deferred Follow-ups / Non-goals

• Exposing normalized channel identity in gateway session context.
• Workspace registry for channel-to-project bindings.
• Guarding repo side effects with workspace bindings.

Review feedback remediation (2026-04-30)

• Confirmed _dm_cache_loaded is used so non-DM rooms do not repeatedly refresh m.direct account data on every message.
• Hardened m.direct cache parsing to ignore non-string room IDs instead of coercing unexpected values into strings.
• Added regression coverage for non-string m.direct entries.
• Added DM cache refresh hardening for newly joined/invalidated rooms so long-running Matrix adapters do not keep stale DM classification forever.
• Updated the test plan to remove stale/malformed counts and show the latest fresh 12-test identity/cache verification.

Relationship to follow-ups

This is the Matrix-specific foundation fix. It ensures named two-person Matrix project rooms are exposed as named rooms, not inferred DMs, before the model sees session context.

Follow-ups:

• feat(gateway): expose normalized channel identity #17711 exposes normalized channel identity generically across gateway platforms.
• feat(gateway): guard repo side effects with workspace binding #17938 consumes channel/project identity to guard repo side effects.

This PR intentionally does NOT add workspace binding or repo side-effect guards.