refactor: sweep the platform-and-sign-in epic

Split load_config into per-section readers, use contextlib.suppress and a single condition where ruff asked, remove stale noqa comments, add the SIM and RUF100 rules, share the sign_in test helper, align AD-6 with the code and record the remaining deferred findings.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N3t4WL7bd9bdHHNjEsxzqC

_bmad-output/initiative-ping-mee-portal/deferred-work.md

@@ -2,5 +2,5 @@
   summary: ARCHITECTURE-SPINE AD-2 says the service account's read rights are limited to a list, but Active Directory gives authenticated users broad read by default, so the statement is not enforced by the test-environment setup.
   evidence: The setup script grants only write rights and the Change Password right; read access is the default. Either soften AD-2 ("needs no more than this list") or enforce it with deny entries; decide when the architecture is next updated.
 - source_plan: `_bmad-output/initiative-ping-mee-portal/epic-platform-and-sign-in/story-audit-throttle-and-session-foundations-plan.md`
-  summary: ARCHITECTURE-SPINE AD-6 names `end_sessions(username, except_current=bool)`, but the built function is `end_sessions(user, except_session_key=None)`.
-  evidence: A function that keeps the current session needs that session's key; a boolean cannot say which one. Reword AD-6 to match when the architecture is next updated; callers use the key form.
+  summary: Concurrent writers on the throttle counters are not tested.
+  evidence: The test database is SQLite in memory with a shared cache, which answers "table is locked" to a second writer at once, so a threaded test fails for reasons that say nothing about production (a WAL file database with a 20 s busy timeout and IMMEDIATE transactions). A real test needs a file database; tried and dropped in the refactor sweep.

_bmad-output/initiative-ping-mee-portal/epic-platform-and-sign-in/story-refactor-sweep-plan.md

@@ -0,0 +1,39 @@
+---
+title: 'Refactor sweep'
+type: 'chore'
+ticket: '8'
+created: '2026-10-18'
+status: 'built'
+baseline_revision: '20510a7'
+route: 'full'
+route_source: 'auto'
+risk: 'low'
+review: 'quick'
+review_source: 'pinned'
+---
+
+## Intent
+
+**Problem:** Entries 1 to 7 left deferred findings and some code that grew in passes.
+
+**Approach:** Behaviour-preserving clean-ups backed by the existing tests; nothing new for users. Scope pushed out of another story is a new story, not part of this one.
+
+## Triage of the epic's findings
+
+| # | Finding | Source | Verdict | Result |
+|---|---------|--------|---------|--------|
+| 1 | `load_config` has 98 statements and 30 branches | sweep (ruff C901, PLR0915) | patch | Split into `_Reader` and one function per section (core, debug, trusted proxies, directory, OIDC, SMTP); `load_config` is 10 lines. Same messages, same tests. |
+| 2 | `try/except/pass` around `unbind_s` twice; a nested `if` in the key cache | sweep (ruff SIM) | patch | `contextlib.suppress`; one condition. |
+| 3 | Unused `noqa` comments | sweep (ruff RUF100) | patch | Removed the stale ones; the two that are still needed (S107, S310) stay. |
+| 4 | Lint rules that would have caught 2 and 3 are not on | sweep | patch | `SIM` and `RUF100` added to the ruff rules. |
+| 5 | `sign_in` test helper lived in `test_signin.py` and was imported by another test module | sweep | patch | Moved to `portal/tests/helpers.py`. |
+| 6 | AD-6 names `end_sessions(username, except_current=bool)`; the code has `end_sessions(user, except_session_key=None)` | deferred from entry 3 | patch (document) | AD-6 reworded to match the code. |
+| 7 | AD-2 says the service account's read rights are limited to a list; Active Directory gives authenticated users broad read | deferred from entry 2 | defer | Needs the owner's decision: soften the sentence or enforce with deny entries. Stays in `deferred-work.md`. |
+| 8 | Concurrent writers on the throttle counters are not tested | deferred from entry 3 | defer | A threaded test fails on the in-memory test database for reasons unrelated to production; tried and dropped. Recorded in `deferred-work.md`. |
+| 9 | Dead code | sweep (vulture) | none | Everything flagged is a framework hook, a setting, or an interface used by later epics. |
+| 10 | Docker build and browser look of entries 6 and 7 | "not verified" in the plans | closed | Checked on the Linux host by the owner (build, shell, test e-mail). |
+
+## Implementation Notes
+
+- `pytest` 319 passed, 6 skipped; `ruff check` clean with the two new rule sets.
+- Nothing outside the epic's code was touched except the AD-6 sentence in the spine and `deferred-work.md`.