fix(tui): preserve custom provider identity on resume

[teknium1]

Summary

Desktop/TUI session resume now preserves named custom provider identity instead of persisting only the resolved custom provider.

Changes

• runtime_provider: add a base_url → custom:<name> lookup across providers: and custom_providers: entries.
• tui_gateway: persist named custom provider identity in session model_config and heal legacy rows that only stored bare custom by using the saved base_url.
• Tests: cover provider identity lookup, persistence, resume round-trip, and legacy-row healing.

Validation

Check	Result
scripts/run_tests.sh tests/hermes_cli/test_custom_provider_identity.py tests/tui_gateway/test_custom_provider_session_persistence.py	12 passed
isolated no-creds E2E _runtime_model_config → _stored_session_runtime_overrides → _make_agent	persisted custom:mimo-v2.5-pro; resolved entry API key

Fixes #44022.
Salvages the focused fix from #44109; #44402 is already on main and #44061 is a broad rollup, not the merge vehicle for this bug.

Infographic

[github-actions]

🔎 Lint report: hermes/hermes-0a703936 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: 10887 on HEAD, 10887 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 5710 pre-existing issues carried over.

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

[teknium1]

Closing as superseded by PR #45578, which merged the same custom-provider Desktop/TUI resume fix onto current main.