Read DSH session format v4 written by dsh 0.2.0-rc.2

[ozymandiashh]

Summary

Fixes #1584.

@deepseek-ai/dsh 0.2.0-rc.2 writes session.v4.jsonl.zstd, so discovery skipped every DSH session with skipping DSH sessions written in session format version 4; upgrade codeburn and DeepSeek Harness contributed no usage anywhere.

This admits format v4 after the semantic reader update the docs prescribe for format bumps, not by relaxing the check:

• Verified the reader's whole consumption surface against DSH's official sessionFormatCatalog (recovery: 'strict', validation: 'current', @deepseek-ai/dsh-session-format-catalog@0.2.0-rc.2): dense seq, usage at assistant/message's data.usage (which gains an informational totalTokens sum this parser ignores) or its embedded stream, the tagged session/end-seed inheritance rule, and llm/retry-started attempt slots are all unchanged in v4. The restore of the fixtures and of a real 0.2.0-rc.2 log both pass strict/current validation.
• What v4 does change — tool-result messages lifted to role tool, unknown tags namespaced plugin:<name>, surfaceOp append/replace metadata, new header fields (agentPreset, origin), untagged session/end-seed markers that unseeded sessions now also write — is either ignored by the reader or already handled by it (the seeded/unseeded consistency checks key on the inherited tag, which v4 keeps as the only inheritance marker).
• Adds v4.jsonl / v4-retry.jsonl fixtures with the same buckets as v0-v3 (uncached input 100, output 20, cache read 30, write 5) and extends the per-version parse tests (totals, retry accounting, embedded-stream preference, tagged inherited-prefix exclusion) to v4. The session.v4-as-unknown-version discovery test moves to v5.
• Bumps PROVIDER_PARSE_VERSIONS.dsh so cached skip-era sessions recompute.

Testing

• npx vitest run tests/providers/dsh.test.ts — 86 passed (including the new v4 variants).
• Full suite passes (three unrelated CLI tests flake on timeouts under full-suite load here and pass in isolation).
• Real 0.2.0-rc.2 log (~/.dsh/sessions, one session, 119 events):

$ npx tsx src/cli.ts doctor --provider dsh --json
  "provider": "dsh", "status": "ok", "candidatesFound": 1,
  "sampled": 1, "parsedOk": 1, "parseFailed": 0, "verdict": "OK (1 session)"

$ npx tsx src/cli.ts overview --provider dsh
  Tokens  123,002   Calls  12   Cache hit  90.1%
  Input 11,783 · Output 3,699 · Cache read 107,520

The parsed totals match the official catalog artifact for the same log exactly (sum of its 12 assistant/message usage records).