Complete correspondent search and add an evidence-backed history command

[jmcte]

Objective

Make the first promised operator job genuinely useful: “What is my history with this person?”

Current search filters sender only and omits participants, labels, flags, and attachment summaries from results. Messages where the correspondent is only a recipient are therefore missed.

Relevant code

• src/mailplus_intelligence/index_writer.py:236-318
• src/mailplus_intelligence/cli.py:54-110
• docs/index-query-contract.md
• README.md:141-148

Scope

• Search a correspondent across from, to, cc, and optionally bcc roles.
• Add recipient/domain, label, flag, mailbox/folder, date, attachment, and thread filters with composable semantics.
• Hydrate result rows with participants, labels, flags, attachment metadata summary, thread confidence, and locator status.
• Add stable pagination/cursor behavior rather than a bare unvalidated limit.
• Add mpi history <address-or-domain> that presents a chronological/thread-grouped metadata timeline.
• Show source locators and explicit missing/ambiguous locator states.
• Keep raw bodies out of search results.

Non-goals

• No semantic relationship graph or inferred person merging.
• No raw full-text body search.
• No automatic contact identity merge across aliases.
• No remote UI.

Acceptance criteria

• Correspondent search finds messages in every participant role.
• Domain and exact-address matching semantics are documented.
• Filters compose predictably and validate bad input.
• Results include the fields promised by the index query contract.
• Pagination is stable under repeated reads.
• mpi history groups/orders messages deterministically and prints locators.
• Missing/ambiguous locators remain visible for review.
• Query plans/indexes are inspected against a representative synthetic corpus.
• Tests cover participant roles, compound filters, pagination, empty results, and privacy boundaries.

Validation

PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=src python3.12 -m unittest tests.test_index_writer tests.test_cli -v
bash scripts/ci/run-fast-checks.sh

Dependency notes

Depends on the unified ingest/thread/reconciliation model. API design can begin in parallel, but implementation should not duplicate temporary thread or participant rules.

Exact dependencies

Implementation depends on #107. Query and CLI API design may begin earlier, but must not duplicate temporary participant or thread semantics.

Parent

Part of #98.