fix: correct marker classifications per repo standard

Reclassify 4 markers that did not match their actual urgency per
docs/development.md:

  TODO → XXX (someday-maybe, no commitment):
    vendor/cordis/src/reflect.ts:250  — enhance error message
    packages/bash-local/src/run.ts:248 — stateful-shell design reference

  FIXME → TODO (should fix soon, not blocking release):
    vendor/loader/src/index.ts:108     — merge config
    vendor/cordis/src/fiber.ts:376     — internal/fiber-info

packages/bash-local/src/run.ts

@@ -245,7 +245,7 @@ export interface RunningBash {
  * RESOLVES with a {@link SpawnOutcome} describing what happened, so callers
  * shape one consistent report for the model.
  *
- * TODO(stateful-shell): per the agent-tool survey there are two proven
+ * XXX(stateful-shell): per the agent-tool survey there are two proven
  * stateful designs worth revisiting — Claude Code persists ONLY cwd between
  * calls (captures `pwd -P` after each command), and Codex keeps whole PTY
  * exec sessions addressable via session ids + stdin writes. We deliberately