Problem

The hashline formatter cache used a single global variable not keyed by directory. The first project's formatters won for all subsequent projects in the same process. Transient config failures were also cached permanently.

Fix

• Key the formatter cache by project directory
• Don't cache transient config.get() failures
• Added regression test for multi-project isolation

Review

All 5 review-work lanes passed (goal, QA, code quality, security, context mining).
Tests passed, typecheck passed, build passed.

Summary by cubic

Scopes the hashline formatter cache by project directory and avoids caching transient config failures. This prevents one project's formatter settings from affecting others in the same process.

• Bug Fixes
  • Cache formatters per normalized directory to isolate projects.
  • Do not cache when config.get() errors or returns no data; retry on next call.
  • Added tests for multi-project isolation and non-caching of failures.

^{Written for commit 6da4d2d. Summary will update on new commits.}