[spark-compete] fix: redact SPARK_HOME path from purge safety error message

[Esc1200]

spark-compete-hotfix-v1

packet: spark-compete-hotfix-v1
team: drophub_sir (esc1200, drophub_sir, spark-agent)
pr_author: Esc1200
repo: vibeforge1111/spark-cli
owner_surface: spark-cli

actual_behavior

safe_spark_home_for_purge in cli.py line 973 raises SystemExit(f"Refusing to purge unsafe Spark home path: {resolved}") which includes the fully resolved internal SPARK_HOME filesystem path in the error message. This leaks the user's home directory layout and internal Spark installation path to stderr.

expected_behavior

The error message should indicate that the purge was refused because the configured Spark home resolves to a system-critical directory, without disclosing the actual filesystem path.

repro_steps

1. Set SPARK_HOME to the filesystem root, user home, or repo root.
2. Run spark setup --purge or any command that triggers safe_spark_home_for_purge.
3. Observe the SystemExit message includes the full resolved path, e.g., Refusing to purge unsafe Spark home path: /home/user.
4. Note that the internal SPARK_HOME path is exposed in stderr output.

before_after_proof

Before: raise SystemExit(f"Refusing to purge unsafe Spark home path: {resolved}") leaks the full resolved SPARK_HOME path.

After: raise SystemExit("Refusing to purge unsafe Spark home path. The configured Spark home resolves to a system-critical directory.") uses a generic message with no path disclosure.

tests_or_smoke

Verified via git diff that the single-line change replaces the path-leaking f-string with a generic message. Python syntax check passed (lint OK). No new imports required. No control flow change.

duplicate_notes

Searched open PRs and branches for a similar fix to safe_spark_home_for_purge path leak. Related path-leak PRs exist for other surfaces (secret-path-leak, manifest-path-leak, error-explain-path-leak) but none address this specific purge safety error message.

risk_notes

Very low risk. The only change is replacing an f-string error message with a static string. The exception is still raised with the same type (SystemExit). No control flow change. No new imports required.

review_claim

impact_claim: medium
evidence_types: git_diff, lint_check
review_state_requested: pr_review