fix(preprocess): parse shared exchange ticker lists

[pengpengyi92]

Summary

• parse parenthesized comma-separated ticker lists that share a supported exchange prefix
• stop shared-prefix parsing at semicolons, conjunctions, and closing parentheses
• define reconstructed EXCHANGE: SYMBOL raw values for additional list members
• add deterministic regression coverage for the five public shapes from the issue, plus a focused example and design documentation

Related Issue

Closes #108

Verification

• pytest -o addopts='' tests/preprocess/test_news.py -q - 20 passed, 8 subtests passed
• ruff format --check . - passed
• ruff check . - passed
• basedpyright - passed with 0 errors
• lint-imports - 7 contracts kept, 0 broken
• python examples/preprocess/02_news_ticker_lists.py - emitted both EVEX and EVEXW
• Full pytest --cov on Windows reached 84.05% coverage with 322 passed and 13 pre-existing platform failures involving SQLite temporary-file locks and LiteParse artifact paths; this draft relies on the repository's Linux CI for the required deterministic verification.

Checklist

• The title uses English Conventional Commit format: type(scope): summary.
• The related issue or design discussion is linked when applicable.
• bash scripts/verify.sh passes locally; Windows-specific existing failures are disclosed above and Linux CI is pending.
• No live-network component smoke test applies because this change is deterministic parsing only.
• Public behavior has focused tests, an example, and documentation where applicable.
• The PR is complete, small, and contains no unrelated changes.

[keli-wen]

Requesting changes. Thanks for taking on #108 — the intent is right, but the shared-prefix extension as written is a net regression, and I don't think this change should carry a new example or a design-doc rewrite. Details below.

Blocking: the shared-prefix scan over-captures ordinary prose

The continuation loop keys off match.end() and then searches for the next ) anywhere in the text (scan_text.find(")", match.end())). When the main regex already matched a balanced (EXCHANGE: SYMBOL) — it consumed its own closing paren — the loop still runs and scans past that paren into unrelated following text. Because _SHARED_EXCHANGE_SYMBOL_RE is compiled with re.IGNORECASE, an ordinary lowercase word right after a (EXCHANGE: SYMBOL), is captured as a ticker.

This flows straight into preprocess_news_document (ticker_hints, news.py:330), so it pollutes real output. On current master the input below yields one hint; on this branch it yields a bogus second one:

# (symbol, exchange, raw) projected from each returned NewsTickerHint
>>> extract_exchange_ticker_hints("Shares of (NYSE: IBM), and (NASDAQ: AAPL) rose today.")
('IBM',  'NYSE',   '(NYSE: IBM)')
('AND',  'NYSE',   'NYSE: AND')      # <- "and" captured as ticker "AND"
('AAPL', 'NASDAQ', '(NASDAQ: AAPL)')

The trigger — a balanced (EXCH: SYM), followed by any later ) — is extremely common in PR-wire prose, so this regresses far more documents than the ~1 warrant of recall that #108 estimates it recovers. The added tests only assert the five happy-path shapes from the issue and never exercise this case, so CI stays green while the regression ships.

Related smell: raw is meant to be the literal matched substring (provenance), but continuation members set raw=f"{exchange}: {symbol}" — a string that never appears in the source (NYSE: EVEXW is reconstructed) — while the first member keeps a dangling (NYSE: EVEX. The tests encode both, which locks that broken raw contract in.

This change should not add an example

extract_exchange_ticker_hints already exists and is already demonstrated end-to-end by examples/preprocess/01_news_pr_wire.py. Extending an existing operation's parsing coverage is a fix, not a new public operation, so it should ship regression tests rather than a second example file. Please drop examples/preprocess/02_news_ticker_lists.py. We'll also tighten the contributor guidance so the "ships with an example" expectation is scoped to new public operations, not edge-case extensions.

The contexts/ doc change is questionable here too

Whether a parsing edge-case should rewrite contexts/design/flow/news.md is debatable — unless this actually changes a documented contract, the design doc probably shouldn't move. It is also the only real merge conflict with master right now (#130 rewrote that file), so dropping the doc change both narrows scope and clears the conflict.

Suggested path

Narrow this to what #108 is actually worth: keep the existing simple/balanced capture and add regression tests that pin the boundary — the first symbol of a shared-prefix list is captured, and (EXCH: SYM), ...) does not over-capture. If we would rather not carry the heuristic at all, deprecating ticker_hints is a reasonable alternative; happy to discuss which way you'd prefer.

Note: I pushed a small chore: normalize CRLF line endings to LF commit to this branch. The files were saved with CRLF, which made the diff look like a full-file rewrite; it now reads as ~+89/-4 against the merge base.