[BUG] Cosmos P2: Lease cleanup endlessly retries already-absent items #51137

Describe the bug
Alan Zimmer's November 6, 2026 audit of com.azure:azure-cosmos:4.84.0-beta.1 reports that both PK and EPK lease cleanup implementations assign effectiveSubStatusCode using getStatusCode() rather than getSubStatusCode(). A normal per-item 404/0 bulk-delete response is therefore interpreted as 404/404, never removed from the pending set, and repeatedly deleted. This can hang migration startup and issue unnecessary requests. Reported priority: P2.

Exception or Stack Trace
No stack trace supplied. Relevant response: non-null per-item status/substatus 404/0.

To Reproduce
Have lease cleanup receive a non-null 404/0 bulk-delete response for an already-absent lease. Check whether the item leaves the pending set and cleanup completes after one delete call. Cover both PK and EPK implementations. This is a proposed regression scenario, not a runtime reproduction from the audit.

Code Snippet
Not supplied. Reported locations: PK LeaseStoreManagerImpl.java:258-275 and EPK LeaseStoreManagerImpl.java:262-279 in the audited source.

Expected behavior
An already-absent lease with 404/0 is treated as successfully cleaned up; processing terminates rather than retrying indefinitely.

Screenshots
N/A.

Setup (please complete the following information):

• OS: Not reported.
• IDE: Not reported.
• Library/Libraries: com.azure:azure-cosmos:4.84.0-beta.1.
• Java version: Not reported.
• App Server/Environment: Change Feed Processor lease cleanup during migration; PK and EPK implementations.
• Frameworks: Not reported.

Dependency mismatch: Not indicated; dependency tree/logs were not supplied.

Additional context
Proposed fix from the audit: use getSubStatusCode() when assigning effectiveSubStatusCode in both copies.

Regression coverage: verify that a non-null 404/0 response completes cleanup after exactly one delete call in each implementation.

Evidence: Alan source-traced this finding through callers and recovery paths; it was not runtime-reproduced. No live Cosmos calls or full SDK test suite were run, and no repository files were changed. This issue tracks validation and implementation of the proposed fix, not an already-applied fix.

Information Checklist

• Bug Description Added
• Repro Steps Added
• Setup information Added