fix(hub): dollar-quote-aware SQL migration splitter

[finedesignz]

Bug

hub/src/db/migrate.ts split schema.sql on ; without respecting PostgreSQL's \$\$...\$\$ dollar-quoted string syntax. Every DO \$\$ BEGIN ... EXCEPTION WHEN ... END \$\$; block got split mid-string. Production boot logs:

[migrate] failed: DO \$\$ BEGIN ALTER TABLE users ADD CONSTRAINT users_claude_session_threshold_pct_range ... — unterminated dollar-quoted string at or near "\$\$ BEGIN ..."
[migrate] failed: EXCEPTION WHEN duplicate_object THEN NULL; END \$\$ — syntax error at or near "EXCEPTION"
[migrate] applied 135/142 statements

Net effect: 7/142 statements failed. Two CHECK constraints (users_claude_session_threshold_pct_range, users_claude_week_threshold_pct_range) and the re-added scheduled_task_runs_status_check never landed.

Fix

Replace naive split(';') with a state-machine splitter splitSqlStatements() that respects:

• \$\$ ... \$\$ and tagged \$tag\$ ... \$tag\$ dollar-quoted strings
• single-quoted strings ('...') with '' escape
• double-quoted identifiers ("...") with "" escape
• line comments (-- ... \n)
• block comments (/* ... */), nested per Postgres semantics
• bare positional params like \$1 (NOT a dollar-quote tag)

schema.sql is not modified — the DO blocks are valid SQL; only the parser was wrong.

Test coverage

13 new unit tests in hub/test/migrate.test.ts:

• DO block with EXCEPTION + inner semicolons → 1 statement
• CREATE TABLE → DO block → CREATE TABLE → 3 statements
• Tagged \$body\$ ... \$body\$ with embedded ; in a string literal
• Single-quoted string with embedded ;
• Escaped '' inside string literal
• Double-quoted identifier with embedded ;
• Block comment containing ;
• Line comment containing ;
• Bare \$1 positional param not treated as a dollar quote
• Nested block comments
• Real-file validation: every DO block in the live schema.sql now parses to a single statement with balanced \$\$ token counts

All 13 pass. No regressions in the rest of the hub test suite (5 pre-existing failures in insert-run-started-at.test.ts are unrelated and exist on main HEAD prior to this branch).

Follow-up flagged (NOT in this PR)

runMigrations() currently catches per-statement errors and continues, only logging them. That silent-failure mode is what let this bug live in production. Worth a separate PR to abort boot on any migration error — but out of scope here per the task brief.

Verification

• bun test test/migrate.test.ts → 13/13 pass
• bun test (full hub suite) → 295 pass, 63 skip, 5 pre-existing unrelated fails

🤖 Generated with Claude Code