docs(spec): define LongHorizon evidence boundary

[aaaazqh]

Story #78

Define the future evidence qualification boundary in docs/specs/2026-08-19-78-longhorizon-run-evidence-boundary.md.

Validation covers the focused doc-link tests, canonical doc-link generator with zero graph change, and diff checks confirming the spec is the only added file.

Summary

Why

• Issue/Story:
• User or maintainer outcome:

Traceability and Scope

• Spec/ADR, if applicable:
• Acceptance criteria addressed:
• Canonical owners changed:
• Explicit non-goals:

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

Manual or visual evidence:

Risk and Recovery

• Compatibility and cross-platform impact:
• Package, plugin, schema, or generated-file impact:
• Rollback or recovery path:
• Residual risk or unverified boundary:

AI Involvement

• Level:
• Human review and 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.

[phodal]

Hi @aaaazqh the issue #78 already assigned, I will close this PR