The tool-output spill capability seam: an abstract storage interface, a local filesystem implementation, and the tool-result policy that uses it. All product packages.

Package	Role	ctx key
`spill/`	Abstract spill storage seam (`saveText` — persist oversized tool text and return a locator + retrieval hint)	`ctx.spillStore`
`spill-local/`	Local-filesystem backend: private, session-scoped files with traversal-safe names	(registers on `ctx.spillStore`)
`spill-policy/`	`tools/post-execute` policy: replaces oversized plain-text results with a preview + spill locator	(no service surface)

The interface lives at spill/spill/. The split mirrors bash/fs: the seam owns storage only, spill-local owns the filesystem mechanics, and spill-policy owns WHEN to spill and the model-facing notice. Preview mechanics stay in util/retention — the policy composes the two without either owning the other's job.

See the tool output spill RFC for the design rationale, including why final-result spill is separate from tool-owned early spill (bash streams, subagent rollouts) and why creation belongs to the runtime spill seam rather than the model-facing write tool.