[m15] containerstdout: backfill 5 deferred failure-mode SKIPs

[trilamsr]

Summary

Phase 13.6 (PR #158) backfilled 10 of 15 `TestFailure_*` stubs. 5 remain as `t.Skip("Phase 14 integration glue: ...")` in `components/receivers/containerstdout/failure_modes_test.go`. Phase 14 plumbing now exists; the gating reason no longer holds.

Skipped tests

1. `TestFailure_FdHygieneAfterPodTermination` — covered by separate issue [m15] containerstdout: fd-hygiene lsof golden missing — MILESTONES claim unsubstantiated #161 (lsof golden).
2. `TestFailure_PodEvictionTailFlush` — needs tailer + stitcher + pod-deletion event wiring (all present now).
3. `TestFailure_RotationStalledSurfacesKind` — partially covered by `TestTailer_RotationStalledKind`; the no-flapping-per-poll axis still missing.
4. `TestFailure_BackpressureDropOnSlowConsumer` — needs receiver + consumer integration (pipeline_test harness available).
5. `TestFailure_FingerprintCardinalityOverflow` — needs tailer-pool fingerprint LRU (Phase 14 wired tailer-pool but no fingerprint cardinality eviction yet — investigate whether this is in scope or a Phase 17 item).

Why load-bearing

Each SKIP is a named contract pin (AGENTS.md lesson #8). A SKIP'd contract is a contract that can drift undetected. Either backfill or remove the identifier with a written rationale.

Affected files

• `components/receivers/containerstdout/failure_modes_test.go`
• New `components/receivers/containerstdout/failure_modes_integration_test.go` (recommended split)

Origin

PR #158, Phase 13.6 deferred 5 of 15 stubs.

[trilamsr]

Outdated by RFC-0013 distribution-first pivot (docs/rfcs/0013-distro-first-pivot.md §2 adoption matrix). containerstdout receiver replaced by upstream filelogreceiver + container stanza + file_storage extension; cursor persistence, fd hygiene, goleak, and failure-mode coverage all become upstream concerns. If pilot deployment surfaces before v0.2.0 cut, reopen with re-evaluation trigger.