remove compat dual-writes from change state store #29

Skein currently maintains a duplicate runtime state location: the primary .skein/changes/<slug>/ AND a compat mirror openspec/changes/<slug>/.skein/ via NewWithCompat. This creates confusion, stale state, and makes the codebase harder to understand.

The goal is to have ONE source of truth: .skein/changes/<slug>/ for Skein runtime state, and openspec/changes/<slug>/ for OpenSpec planning content (proposal.md, tasks.md, specs/). No duplication.

Current state:

• NewWithCompat(runtimeBase, specBase) in defaults.go writes to both locations
• HasFlag, FlagMtime read from both (primary first, compat fallback)
• SetFlag, ClearFlag, SetBlocked, WriteTextFile, AppendTextFile, SetPriority write to both
• isInitializedChange in openspec/load.go checks for .skein/ in the openspec dir as a marker
• resolveStatus in openspec/load.go has store-first path + legacy file fallback
• resolveStatusWithStore in auditor/auditor.go has store-first path + legacy file fallback
• Migrate command exists to copy state from compat→primary

What to do:

1. Remove compat writes — Change NewWithCompat to New in defaults.go and all callers. Remove the specBase field and all compat write logic from file_store.go.

2. Update isInitializedChange — Instead of checking for .skein/ in the openspec dir, check if .skein/changes/<slug>/ exists (via changestate.Current().RuntimeDir(slug)). Keep the proposal.md / tasks.md checks for hand-authored changes.

3. Remove compat reads — Remove the compat directory fallback from HasFlag, FlagMtime in file_store.go.

4. Remove legacy fallback — In resolveStatus in openspec/load.go, remove the legacy file check fallback and only use the store path. Same for resolveStatusWithStore in auditor/auditor.go.

5. Run the Migrate command on existing repos to copy compat state → primary, then clean up the compat directories.

6. Update tests — Tests that use NewWithCompat should use New. Tests that check for compat writes should be updated.

7. Clean up comments — Remove references to "Slice 8" and "compat" and "legacy" throughout.

Key files:

• internal/port/adapter/defaults.go — change NewWithCompat to New
• internal/infra/changestate/file_store.go — remove compat logic
• internal/openspec/load.go — update isInitializedChange, remove legacy fallback
• internal/auditor/auditor.go — remove legacy fallback
• internal/cli/intake_test.go — update test
• internal/cli/migrate_state.go — can be simplified/removed after migration

Caution: This is a breaking change for repos that have only compat state. The Migrate command should be run first on existing repos.

Disposition (2026-09-18)

Archived — superseded/obsolete. Misfiled — targets the skein Go repo (internal/port/adapter, changestate).