himalaya/cairn/changes/capability-shared-api/tasks.md

cairn	change
tasks	capability-shared-api

Tasks

• Capability enum + per-backend static registry (one declaration site per backend, next to its adapter).
• Resolver: verb -> capability -> configured transport, with --backend as filter and explicit override; assert it reproduces today's select_storage order for every existing shared verb.
• Dynamic tier: per-client capability probe (IMAP CAPABILITY, JMAP session, ManageSieve SIEVE) consulted only after connection, only for verbs that need it.
• Capability error type: account, resolved backend, missing capability, protocol-specific alternative; non-zero exit, printed like every other error.
• Ungate the clap tree from cargo features, keep dispatch gated; confirm json-schema output is identical for --no-default-features and full builds.
• Generate the per-command backend support annotation into --help and the manual from the registry.
• Compatibility suite: every existing shared command's stdout (table + --json) unchanged against 2.x for each backend.
• nix develop --command cargo build/test --bins; reduced-feature builds; cargo fmt; clippy clean.
• MIGRATION.md note: new capability error replaces unknown-subcommand for unsupported verbs; nothing removed.
• Rewrite the cairn/spec/commands.md opening paragraph: the shared API is a capability union held coherent by one-meaning-per-verb, no longer the least-common-denominator intersection.
• Fold delta.md into cairn/spec/commands.md and cairn/spec/backends.md; add cairn/log entry; mark change landed.