fix(export): contain spreadsheet formula interpretation in session CSV

[seonghobae]

Finding

The sessions CSV exporter quoted delimiters/quotes but did not treat spreadsheet formula interpretation as a separate output-boundary concern. Attacker-controlled session/project text beginning with formula-triggering characters could therefore become a formula when an authorized user opens the export in spreadsheet software.

The prior HIGH/RCE wording was broader than the current evidence. Practical impact depends on the spreadsheet application and user interaction. OWASP documents formula execution/data-exfiltration risks, but also notes that common quote/apostrophe mitigations are not universally reliable after Microsoft Excel save/re-open.

Repair

Current exact head: 1324e1ed2771ab10dfc87ac34833cdb4b6220581
Protected target at repair start: developmental@2fa92012bcf80acc1f921a4bafea76b3b1424b46.

Effective product delta is intentionally scoped to:

• packages/web/src/lib/server/csv.ts: pure, documented CSV field serialization boundary with an explicit string return contract;
• packages/web/src/lib/server/csv.test.ts: individually attributable formula-trigger, Unicode/control, delimiter/quote, leading-space and numeric-semantics regressions, aligned with the repository test strategy;
• sessions export route: consumes the shared serializer;
• docs/product-technical-gap-baseline.md: records the code-current boundary, evidence and spreadsheet-application acceptance gap.

Normal repair descendants restored .jules/sentinel.md, root package.json and pnpm-lock.yaml to protected-base authority, removing unrelated dependency overrides and generated doctrine from this security lane.

Acceptance

Keep Draft until the unchanged exact head has terminal-success type/lint/test/security/SAST/CodeQL evidence and current review/thread evidence. Unit tests establish deterministic serializer behavior, not universal spreadsheet safety. Before claiming the buyer-visible gap closed, validate benign payloads in the supported spreadsheet target(s), including Excel save/re-open if Excel is supported, and inspect the raw CSV to prove delimiter/quote inputs cannot create a second cell.

Reference: OWASP CSV Injection — https://owasp.org/www-community/attacks/CSV_Injection

Do not reintroduce unrelated dependency churn, source-neutral retriggers, self-approval, synthetic status, or gate weakening.

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