fix(dsh): support alpha.1 session persistence drift

[Cobb04]

Summary

Keep Better Harness Session analysis compatible with the persisted Session
contract introduced by DeepSeek Harness 0.1.2-alpha.1.

The DSH adapter now validates and expands native range-encoded
sourceEventSeqs and exactly recognizes the three new required persisted
control events without weakening rc.2 compatibility or fail-closed validation.

Why

• Issue/Story: Closes [Bug]: Decode DSH alpha.1 Session provenance ranges and required events #130
• User or maintainer outcome: Valid native DSH alpha.1 raw, zstd, and packed
  Sessions are no longer rejected solely because of the new persistence
  encoding or required control-event vocabulary.

Traceability and Scope

• Spec/ADR, if applicable:
  docs/specs/2026-08-30-130-dsh-alpha1-session-compatibility.md
• Acceptance criteria addressed: AC-1 through AC-10
• Canonical owners changed:
  • scripts/session-analysis/platforms/dsh.mjs
  • test/sessions/session-analysis-dsh-discovery.test.mjs
  • the Story-linked compatibility Spec
• Explicit non-goals:
  Profile/Preset/Cordis runtime resolution, Skill or Instruction changes,
  report semantics, installation changes, dependency changes, capability
  flags, and promotion of alpha.1 to the qualified DSH baseline.

Change Type

• Feature
• Bug fix
• Tests only
• Documentation/community
• Refactor with no intended behavior change
• Dependency, packaging, or infrastructure

Test and Review Evidence

Check	Result
Node 22 DSH Session focused suite	Node 22.20.0: 3 files passed, 112 tests passed, 0 skipped
Node 24 DSH Session focused suite	Node 24.15.0: 3 files passed, 112 tests passed, 0 skipped
npm test	107 files passed, 1,613 tests passed, 2 skipped
npm run harness:generated	PASS; generated-source diff clean
npm run harness:test	20 files passed, 173 tests passed
npm run pack:verify	PASS; 619 npm entries and 881 runtime-zip entries
Spec/doc-link check	1 file passed, 8 tests passed; 39-file/56-link graph unchanged
git diff --check / staged diff review	PASS

Manual or visual evidence:

No visual surface changed. Compatibility qualification used native DSH
0.1.2-alpha.1 Session persistence artifacts for raw, zstd, packed provenance,
and the three new required event types. The pre-fix baseline rejected those
contracts; the final adapter accepts valid native shapes while malformed known
events and unknown required events remain fail-closed.

Risk and Recovery

• Compatibility and cross-platform impact:
  rc.2 scalar provenance remains supported; alpha.1 range provenance is decoded
  only at the DSH physical-storage boundary. Local post-rebase validation covers
  Node 22 and Node 24. Fresh PR CI is the authoritative Windows/Linux/macOS
  cross-platform receipt.
• Package, plugin, schema, or generated-file impact:
  No dependency, package, capability, report-schema, or DSH baseline change.
  The patch only extends the existing format-0 DSH Session persistence adapter.
• Rollback or recovery path:
  Revert this single compatibility commit to restore the prior rc.2-only
  adapter behavior.
• Residual risk or unverified boundary:
  DSH 0.1.2-alpha.1 remains a prerelease/source compatibility target rather
  than the qualified baseline. Do not claim npm-installable alpha support.

CHANGELOG note:
No CHANGELOG entry was added because this does not promote alpha.1 to the
qualified support baseline, and root AGENTS.md restricts task-external
release metadata without explicit Issue/Spec authorization.

AI Involvement

• Level: Assisted
• Human review and validation:
  Cobb04 defined and approved the compatibility boundary, reviewed the
  qualification and independent pre-PR findings, required fail-closed regression
  coverage, and authorized submission after maintainer Issue review. Codex
  assisted with implementation, tests, traceability, and delivery validation.

Checklist

• I followed AGENTS.md, CONTRIBUTING.md, and the relevant canonical-owner guidance.
• The change is focused and does not include unrelated local or generated state.
• Tests and documentation match the behavior actually delivered.
• Markdown links were checked when documentation moved or changed.
• Cross-platform behavior was considered for Windows, macOS, and Linux.
• Package/runtime verification was run when shipped files or dependencies changed.
• User-facing or compatibility changes are recorded in CHANGELOG.md.
• I have the right to contribute this work under the repository's MIT License.