storeReceivedFile's mid-round AfterDephantomize crosslink cascade became context-aware in #166, and the clone and server-push receive paths already pass their real deadline context into it. The third caller -- the general push/pull path -- did not: (s *session) handleFileCard hardcoded context.Background(), so an ordinary Sync could not interrupt a long-running crosslink cascade via its caller's deadline the way a Clone now can.

Thread the sync loop's own context the one remaining hop:

- processResponse gains a ctx parameter and passes it to handleFileCard. - handleFileCard gains a ctx parameter and hands it to storeReceivedFile instead of context.Background(). - Sync's round loop passes its ctx into processResponse.

Existing processResponse callers in tests pass context.Background(), the convention already used elsewhere. A new regression test drives the general sync path (processResponse) with a context cancelled mid-cascade against a fanout large enough to cross crosslinkCancelCheckStride and asserts the cascade stops early rather than crosslinking every child. check-in: 5ef8deb561 user: [email protected] tags: trunk