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Scenario 7: Preview and apply a layer to one or more target harnesses

Use this when you are ready to materialize a known-good setup into a project. The dry-run preview is itself a frequent check before a real write.

Frequency: Common · Status: Shipped

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Use this when you are ready to materialize a known-good setup into a project. The dry-run preview is itself a frequent check before a real write.

Typical commands:

harnesstap layer apply my-setup --project . --harness claude-code,codex,cursor --dry-run
harnesstap layer apply my-setup --project . --harness claude-code,codex,cursor
harnesstap status .

Plugin-version policy when the layer carries plugin pins:

harnesstap layer apply my-setup --strict-plugin-versions   # exit 2 on pin violation
harnesstap layer apply my-setup --ignore-plugin-versions   # skip validation

layer apply is the canonical write path for one or more layers. Stack multiple layers in one command (see Scenario 25).

Important distinction: applying a layer writes a known baseline onto disk. If you later want to sync alias harness outputs from the current on-disk main harness without re-specifying the layer, use harnesstap mirror instead.