ADR 0426: Shared-file markers claim only discern's part

Status: accepted; amends the marker wording of ADR 0211

A comment-capable artifact outside agent context carries a provenance marker. Every marker except the worktree environment file's opened with "Generated automatically by discern via …", whatever the file's ownership.

That wording fits a Generated file, which discern rebuilds whole. A Shared file is different: discern maintains one region, block, or set of entries, and the rest belongs to the project or to other tools. A compatibility probe ran discern beside another tool that writes the same provider configuration. .codex/config.toml held both tools' tables, yet its first line presented every table as discern's output. A reader, or the other tool, could fairly conclude that the file was generated and that edits outside discern's entries would be lost.

The worktree environment file already used a scoped form, "Worktree values managed by discern via …". That form lived beside the shared renderer instead of in it.

A marker's claim follows File ownership. Each comment-capable artifact declares an ArtifactProvenance in src/shared/file_ownership.ts: its source, and for a Shared file, the scope the marker claims. One renderer, artifactProvenanceMarker in src/shared/brand.ts, produces both forms:

• Generated: Generated automatically by discern via <source> | https://discern.sh.
• Shared: <scope> managed by discern via <source> | https://discern.sh, such as "This block managed by …" in .gitignore or "MCP server, writable-root, and doc-size entries managed by …" in .codex/config.toml.

DISCERN_NO_ATTRIBUTION still removes the byline and link from either form and keeps the claim and source.

The registry enforces the pairing. writtenArtifactClass refuses a Shared comment-capable declaration without a scope and a Generated one with a scope. The provenance test renders every registered comment-capable artifact, requires its declared marker, and rejects any file-wide claim in a Shared file.

A rewrite recognizes either claim. isArtifactProvenanceMarker matches both forms for the artifact's source in both attribution modes. A refresh or upgrade therefore replaces a marker written under the other claim with exactly one current marker.

• Reword only .codex/config.toml. The same false claim sat at the top of the Codex environment and rules files and of discern.toml. Fixing one file leaves the class, and the next Shared artifact would copy the old wording.
• Leave block markers as they were. The .gitignore and .gitattributes markers sit inside discern's delimited block, so position already scopes them. A single rule is simpler to enforce than a placement exception, and "This block" says what position only implies.
• Drop markers from Shared files. A reader would then have no in-file pointer to the source of discern's entries, which ADR 0211 keeps for every comment-capable artifact outside agent context.

The next discern refresh rewrites the marker line in .gitattributes and the Codex files; the next discern upgrade does the same for discern.toml and the .gitignore block. Each is a one-line change.

The published generated_marker_prefix convention still identifies Generated files. A tool that recognized discern's files by that prefix no longer sees Shared files as generated, which matches their ownership.

A new Shared comment-capable artifact must declare the part of the file its marker claims before it can join the registry.