Senior Python / AI Backend Engineer

FastAPI, permission-aware hybrid retrieval and data isolation | Freelance

Elchai is preparing one bounded backend retrieval pilot for New Pulse.

Assignment

Extend an agreed existing hybrid-retrieval baseline rather than rebuild it. Validate the approved request/context input; open only authorised collections; enforce the approved record-label constraints inside both semantic and lexical query paths; and pass only permitted extracts to an offline recording model substitute. Preserve relevant existing retrieval behaviour within the allowed scope. Review existing labelling and tests for reuse before writing duplicate work.

Work uses an isolated sandbox, synthetic documents, approved test dependencies and no paid model/provider calls. Elchai supplies or approves the identity/context/evidence interfaces; this role does not invent a policy engine or second orchestrator. Internal owners retain architecture, security policy, independent QA, acceptance and release authority.

Explicit exclusions: full-document reads, attachments and deep-read hydration, downloads and protection of those bypass routes; real-data ingestion, memory migration, frontend/voice work, production tenancy, live services and a whole-platform rewrite. Pilot acceptance is retrieval-only and must not be presented as integrated product security approval.

M0-M4 and smaller checkpoint handovers

Milestone M0

Internal preparation 8-12 h; internal review 4-6 h.

Exact baseline, reuse/non-duplication map, approved allowlist, input/output contracts, tests, dependencies, named reviewer and available hours.

Pass condition: Client completes readiness and records written start approval. No free candidate research/code deliverable is requested.

Milestone M1

16-24 focused implementation h.

M1.1 context checks; M1.2 permitted handles/vector predicates; M1.3 lexical predicates/fusion; M1.4 required evidence/context boundary. Each 4-6 h, with exact checkpoint and smoke evidence.

Pass condition: Both real query paths enforce the approved scope; only authorised files change; no external/production connection.

Milestone M2

12-20 focused test/correction h; separate internal review 4-6 h.

M2.1 positives/regressions 2-4 h; M2.2 negatives 4-6 h; M2.3 concurrency/faults 4-6 h; M2.4 evidence manifest 2-4 h.

Pass condition: All frozen package tests pass; no unexplained failures, missing evidence or unresolved authorisation defect.

Milestone M3

4-8 h reserved corrections; separate internal review 4 h.

Independent replay, functional demo, rollback, clean-start takeover and exact accepted artifact.

Pass condition: Authorised internal acceptance of the stated component only; not permission to merge or deploy.

Milestone M4

4 h reporting/handover; separate internal review 2 h.

Actual hours/worked days/waits/defects; accepted versus unfinished work; next task and comparable next-slice estimate.

Pass condition: Transfer evidence complete and actuals reconciled; no automatic further assignment.

The initial development/test/correction allowance is 32-52 focused hours, excluding M0 preparation, M4 reporting, internal review and waiting time. Quote your own effort, currency, fee, documentation/correction assumptions, available hours and working-time overlap. These planning ranges are not a fixed price, calendar deadline, funded trial or commitment for the complete product.

Verification

The agreed suite covers allowed retrieval, invalid signed context, forbidden collections and labels, lexical-only bypass attempts, content-based authority manipulation, two required evidence writes, unavailable dependencies, concurrent scope changes and regression/rollback. Proposed stress minima are 200 mixed requests in each of three clean runs, 1,000 requests with 10 concurrent callers and 20 repetitions of each defined fault. Required pass conditions include zero unauthorised candidates/model-input canaries and complete per-run evidence. Freeze the exact fixtures, commands, expected outputs and resource limits before work; mocks cannot stand in for both real retrieval legs.

Transfer-ready handover at every checkpoint

Supply the exact candidate version, changed-file manifest, setup/test commands and dependency versions, contracts, fixture hashes, raw evidence, known issues, accepted/unaccepted work and one exact next task. Another authorised contributor must reproduce the checkpoint without your private accounts or undocumented knowledge. No source material or confidential information from former clients is requested.

Evidence requested

Provide two relevant public or appropriately redacted examples with your precise contribution, hybrid-retrieval/authorisation experience, available hours and non-binding milestone quotation. Explain how a vector filter can be bypassed by a lexical path or cache, without supplying former-client confidential code. No code access, confidential specifications, credentials or real data is supplied during tender. No unpaid implementation or paid assessment is requested under this draft.