fix: graph-buffer upsert contract + mem budget poisoning (4 red tests)#923
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The deterministic same-QN collision rule picked the lexicographically smallest (label, file_path, start_line, name), which silently inverted the documented upsert/merge semantics: re-upserting a QN with updated fields kept the OLD content (gbuf_upsert_updates, gbuf_upsert_same_qn_updates_all_fields, gbuf_merge_overlapping_qns all red on every platform). Replace it with a single mixed-direction total order applied in both cbm_gbuf_upsert_node and merge_update_existing: smallest file_path, then LARGEST start_line, then largest name/label. Still a pure content function of the two candidates (commutative, associative, scheduling-independent — multi-threaded runs stay byte-identical, verified by the xfs MT x4 fingerprint guard), and line-descending within a file restores the classic contract: a later definition in the same file replaces the earlier one, and a full tie is the same entity refreshed in place. Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
cbm_mem_init is init-once (guarded by g_initialized), so the backpressure test's setenv(CBM_MEM_BUDGET_MB=1) + re-init 'restore' was a silent no-op: whichever init ran first fixed the budget for the whole process. In the full runner this test's init won, locking a 1 MB budget that leaked into every later budget consumer — mem_over_budget_low_rss red on every platform, and all subsequent pipeline tests silently running with backpressure permanently engaged. Add cbm_mem_set_budget_for_tests(): writes the budget directly without touching the init guard. The test now saves the caller-visible budget, sets 1 MB via the hook, and restores before asserting. Env dance removed. Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>
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Fixes the four cross-platform test failures blocking the dry run:
Local gates: full suite 5922 passed / 0 failed; determinism repro green (only known deliberate REDs remain on the non-gating board); lint-ci clean.