refactor(backend): remove dead modules and the 14 vulture hits (#2493)

[dolho]

Summary

Closes #2493 — the four pieces of backend dead weight removed, with vulture --min-confidence 80 now reporting zero findings and no suppressions added. Two of the fourteen vulture hits turned out not to be dead; per the issue's own rule ("a behaviour change anywhere means the item was not dead"), those were fixed by making the liveness visible to vulture rather than by deleting live code.

The four items

1. utils/errors.py — deleted. grep -rn "utils.errors\|SafeHTTPException\|log_and_raise" src/ tests/ is empty (AC 1).
2. The two OSS-move schema shims — deleted. They had no importer in src/, but seven test call sites across six files used them, which is the AC 2 carve-out: the tests now call one shared applier, tests/conftest.py::ensure_schema_tables(*names), over the canonical db/schema.py DDL (Invariant Feature/vector log retention #3 — index statements matched by table name, preserving the shims' own drift rationale). ent#443's test_the_bootstrap_helper_owns_no_ddl repoints at the conftest helper, so the no-second-copy-of-DDL guard survives the shim it was written about. Placement note: the helper lives in tests/conftest.py, not tests/unit/conftest.py — from conftest import … resolves to the parent (the stubbed_modules precedent), which a first attempt found the loud way.
3. scripts/poc/ — deleted outright (the issue offered archiving the Nevermined demo; git history is the archive, and nothing references the directory).
4. The 14 vulture hits — resolved as:
   • 5 genuinely unused imports dropped: pop_frames (twilio_media_stream — the live copy is in voip_audio), get_portal_identity (router.py referenced it only in docstrings), SlackOAuthInitResponse, PageBreak, and event_bus's RedisResponseError try/except pair (bound, never read).
   • exc_type/tb ×3 are protocol parameters, not the sys.exc_info() unpacking the issue's technical note guessed — they sit in __exit__/__aexit__ signatures and cannot be dropped. Renamed to _-prefixed (idiomatic unused-argument marking, not a linter directive).
   • Coroutine was NOT dead — read by the string annotation "Coroutine[Any, Any, None]" on _spawn_bg, which vulture cannot see. Unquoted the annotation (evaluates fine at runtime; collections.abc generics are subscriptable).
   • NON_ROW_RETENTION_OPS_KEYS's re-export was NOT dead — two tests imported it from settings_service. Repointed them at config (the true home; the sibling re-exports stay, they have production readers) and dropped the one line.
   • old_subscription_id — a dead parameter of _perform_auto_switch; removed from the signature, its one production call site, and six test call sites (all keyword, so the removal is mechanical and total — zero residual grep hits).

Verification

• vulture src/backend --min-confidence 80 --exclude '*/venv/*,*/__pycache__/*,*/tests/*,*/enterprise/*,*/migrations/versions/*' → zero findings, exit 0 (AC 4).
• Residual greps for every deleted symbol/module: empty (AC 1/2).
• 497 tests across every touched suite pass locally (portal exposure ×3-site rewrite, logout block, shared sessions, room budget defaults, delegated identity, rooms-oss-core, all three auto-switch suites, retention edges, headroom history, both VoIP suites, telemetry sharing); full tests/unit run in flight locally and authoritative in CI (AC 5).
• Deletions + test rewiring only; no production behaviour change anywhere (the two "not dead" items are annotation/import-shape changes with identical runtime semantics).

🤖 Generated with Claude Code

https://claude.ai/code/session_01NLfHNPtB5UCMk4LonZiJux

[obasilakis]

/validate-pr: APPROVE

Deletions map 1:1 to the issue's five ACs, and the two "not dead" items were correctly reclassified rather than deleted.

Dead-code verification — the failure mode that actually matters here — is clean. Greps run against the PR head ref:

• utils.errors / SafeHTTPException / log_and_raise / safe_error_message / init_client_portal_schema / init_shared_sessions_schema / client_portal.schema / shared_sessions.schema / PageBreak / RedisResponseError — 0 hits repo-wide.
• Enterprise submodule checked too (public CI cannot see it): its references are to enterprise.backend.{client_portal,shared_sessions}.schema, which are distinct files under src/backend/enterprise/backend/…/schema.py and untouched. No cross-repo break.
• pop_frames — the live copy stays in voip_audio.py:39; twilio_media_stream.py has 0 call sites, so that import is genuinely unused.
• old_subscription_id — removed from the signature plus 1 prod call site and 6 test sites, 0 residual hits.
• Coroutine unquoting is runtime-safe: imported at module scope from collections.abc (task_execution_service.py:23), subscriptable on 3.13.

I also chased the one subtle risk: the new conftest.ensure_schema_tables narrows the old shim's index matcher from "enterprise_portal" in stmt to table(. Safe — every live INDEX statement in db/schema.py:1893-1910 uses the no-space table( form, so no index is silently dropped, and the ent#443 no-DDL guard plus a new idempotency test are repointed at the helper.

Warnings

• pytest (base, seed 99999) is red from a 45-minute job timeout on the BASE (dev) side, not a test failure and not head. All three head seeds are green (8–10 min) and regression diff passes. Needs a re-run, not a code change — but it keeps the merge gate blocked.
• docs/security/OWASP_COMPLIANCE_REPORT.md:243,264,294 still names the deleted utils/errors.py as the A10 remediation, marked "DONE". The control was never actually wired (error_handlers.py owns the 422/500 shape), so the report was already inaccurate — this deletion just exposes it. One line noting the live owner would close it.

Suggestions

• get_portal_identity (client_portal/portal_auth.py:156) now has zero call sites in OSS and in the enterprise submodule — only docstrings and docs reference it. Vulture's <80% confidence threshold missed it; candidate for the next sweep, not this PR.
• tests/unit/test_1073_voip_media_stream_ticket.py:127 patches audio_mod.pop_frames for a path twilio_media_stream never calls — leftover scaffolding.

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Findings produced by /validate-pr (Claude Code).