chore(claim): remove dead DEFAULT_HEARTBEAT_STALE_THRESHOLD constant

[rjwalters]

While reviewing PR #3440, the shepherd-progress branch was correctly removed from _is_claim_abandoned(). However, the constant DEFAULT_HEARTBEAT_STALE_THRESHOLD (defined at line 34 of loom-tools/src/loom_tools/claim.py) was its only consumer and is now unreferenced.

Changes needed

• Remove DEFAULT_HEARTBEAT_STALE_THRESHOLD definition from claim.py (lines 33-36, including the env-var read via os.environ.get)
• Verify no other file in loom-tools/ imports or references this constant

Context

Discovered during evaluation of PR #3440 (chore: remove dead shepherd-progress logic from _is_claim_abandoned()).

[rjwalters]

Curator Notes

Verified the constant is dead in claim.py via git grep DEFAULT_HEARTBEAT_STALE_THRESHOLD — only the definition itself appears, no consumers. Verified all affected paths exist on origin/main per the #3418 rule.

Critical Nuance — Two Constants With The Same Name

There is an identically-named constant DEFAULT_HEARTBEAT_STALE_THRESHOLD in loom-tools/src/loom_tools/orphan_recovery.py:53 that is NOT dead — it has 3 internal references in that module:

• orphan_recovery.py:53 — definition (= 300)
• orphan_recovery.py:144 — return value
• orphan_recovery.py:332 — default kwarg in heartbeat_threshold parameter

This separate module-scoped constant must remain untouched.

Affected Files (verified on origin/main)

• loom-tools/src/loom_tools/claim.py — remove the constant definition and its os.environ.get(...) block at lines 33-36:

  # Default heartbeat staleness threshold: 5 minutes (300 seconds)
  DEFAULT_HEARTBEAT_STALE_THRESHOLD = int(
      os.environ.get("LOOM_HEARTBEAT_STALE_THRESHOLD", "300")
  )

DO NOT TOUCH

• loom-tools/src/loom_tools/orphan_recovery.py — has an identically-named but separate constant that IS used.
• import os in claim.py — still needed for os.getpid() on line 107. Do NOT remove the import.
• LOOM_HEARTBEAT_STALE_THRESHOLD env var contract — still read independently by completions.py:41 and orphan_recovery.py:138. Removing claim.py's read does not break that contract.

Test Verification

grep -n DEFAULT_HEARTBEAT_STALE_THRESHOLD loom-tools/tests/test_claim.py returns no matches on both the current tree and origin/main. No test changes required.

Acceptance Criteria

• DEFAULT_HEARTBEAT_STALE_THRESHOLD constant and its os.environ.get block are removed from loom-tools/src/loom_tools/claim.py
• The identically-named constant in loom-tools/src/loom_tools/orphan_recovery.py is unchanged
• import os line in claim.py is retained (still consumed by os.getpid() at line 107)
• pytest loom-tools/tests/ passes with no regressions
• Net LOC delta: approximately -4 lines (the constant comment + 3-line definition)

Implementation Notes

1. Make the deletion (lines 33-36 plus the immediately-preceding blank line if it leaves a double-blank-line gap).
2. Re-run git grep DEFAULT_HEARTBEAT_STALE_THRESHOLD loom-tools/src/loom_tools/claim.py to confirm zero matches.
3. Re-run git grep DEFAULT_HEARTBEAT_STALE_THRESHOLD loom-tools/src/loom_tools/orphan_recovery.py to confirm 3 matches still present (sanity-check the surgical change).
4. Run pytest loom-tools/tests/test_claim.py -v locally to confirm no test references.

Test Plan

• Run pytest loom-tools/tests/ -v and confirm green.
• Run git grep DEFAULT_HEARTBEAT_STALE_THRESHOLD and confirm only the 4 expected lines in orphan_recovery.py remain (def at 53, return at 144, kwarg at 332 — note grep total of 3 lines, the count is correct).