feat(email-writing): build authorized thread context

[seonghobae]

Scope

This Draft PR implements Task 4 only: server-authoritative email/thread/recipient context construction for the writing-review workflow. It excludes contextual-orchestrator/model execution, Candidate/Judge semantics, review API, Inkspan editor integration, sending, policy publication, and release behavior.

The service keeps owner/organization authorization, canonical thread membership and chronology, complete-message budgeting, recipient-role derivation from persisted headers, trust labels for untrusted content, and fail-closed handling for oversized selected content. It does not infer importance, tone, actionability, or intent from keywords, sender domains, recipient counts, language names, nearest-text search, or positional heuristics.

Live stack state — 2026-09-01

Direct parent #1328 is ea61b9de9cd26a26209da36e858510a31486531a. This Task-4 head is 64d1f746723616b0111eb40b130d6f07ed413a86 and contains that exact parent through an ordinary non-destructive two-parent merge. No force-push or destructive rebase was used.

Its unique Task-4 delta remains the context TDD workflow, email_writing_context_service.py, and the two focused context-service test modules. Current root design documents are inherited through the stack and are not Task-4-owned semantic delta. All predecessor-head evidence is stale after this movement.

Authorization/privacy contract retained

• selected-email and thread lookup remain owner/organization scoped and tenant-indistinguishable on unavailable references;
• browser-supplied thread text, participant roles, endpoints, credentials and semantic selectors are not trusted authority;
• messages are selected as complete canonical units; no byte/grapheme/selector truncation or lexical importance heuristic;
• context-required PII is preserved only under purpose-bound authorization rather than blanket masking;
• raw context, prompt and model outputs remain excluded from ordinary evidence/log surfaces.

Evidence and continuation

Fresh exact-head authorization/isolation, Python 3.14, coverage/docstrings, SAST/security/dependency/package/provenance and review/thread evidence must be regenerated for 64d1f746723616b0111eb40b130d6f07ed413a86. Child #1356 is reconciled onto this exact Task-4 head as beb28466573b2163df97b027a6d3ac3776773869; later task-owned descendants have likewise been advanced in dependency order. No predecessor evidence transfers.

Merge boundary

Keep Draft while current-head evidence is regenerated. Merge only on an unchanged head satisfying live rulesets/protection, every applicable exact-head gate, zero valid unresolved findings, and any qualifying independent approval actually required after the last push. Pending/queued/skipped-required/cancelled/neutral/failed/absent/stale/predecessor/synthetic/model-only/status-only/author-only evidence is non-passing.

No writing-guidance feature is shipped by this context slice; editing and sending remain available.

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📥 Commits

Reviewing files that changed from the base of the PR and between ea61b9d and 64d1f74.

📒 Files selected for processing (4)

• .github/workflows/email-writing-context-tdd.yml
• backend/services/email_writing_context_service.py
• backend/tests/test_email_writing_context_service.py
• backend/tests/test_email_writing_context_service_coverage.py

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[seonghobae]

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[github-actions]

PR governance metadata gate is not ready for 64d1f746723616b0111eb40b130d6f07ed413a86:

• Draft PR: merge automation is paused.

[seonghobae]

@coderabbitai review

Please review the unchanged exact current head 4570747ccebd57ccaab30ffc68239f0c9d2f1ca0 (normal merge of live parent #1328 51fb5e85). Predecessor 0376d0ac evidence does not transfer. Local Task 4: 32 focused context tests passed, 100% coverage. Keep Draft. This comment is not an approval.

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@seonghobae I will review the exact current head 4570747ccebd57ccaab30ffc68239f0c9d2f1ca0. The PR remains Draft. This action does not approve or merge the PR.

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