pi-posthorse context-window extension

Type: types/note.md

Evidence basis: extension source and shipped documentation at commit 5bdba3536e186a7be845844d0398c3485a7f8e2b, inspected 2026-09-25. No package execution or provider experiment was performed.

Posthorse supplies context-window policy for a required Pi fork: stable guidance, checkpoint reminders, explicit and automatic rollover requests, notes, and history retrieval. The extension is a complete artifact in a partial host loop. Pi owns journal persistence, projection and atomic window commits; those guarantees remain documented external contracts. The Codex adapter prototype, external host implementation and deployed agents are excluded.

The host loads the extension, which checks required native APIs. Before model work it adds context-management guidance. The model can read/write notes, retrieve transcript entries, inspect remaining capacity or request a new window. Near the threshold a best-effort reminder may prompt checkpointing; the automatic hook instead extracts bounded recovery text from the current branch and projection. A returned request does not establish that Pi committed it. Unsupported APIs throw, oversized explicit handoffs are rejected, and nonfitting automatic recovery leaves host behavior in control. These are source-wired paths in index.ts.

Automatic recovery prioritizes owner input and eligible tool receipts, records provenance, bounds text and points back to history. It warns that previous work may already be finished. Context edits affect selected recovery; stale reminder fingerprints suppress active guidance while raw records remain. This is a trace-fed write route even without a model-generated summary, but durable delivery to a later window is host-claimed. Windows and branches do not establish its task horizon. Selection and character-based budgeting are implemented in recovery construction.

Notes accept authored text, whole-file replacement and append; legacy import preserves existing destination files. History pull uses lexical query or identity, with current-branch or project-attributable session scope. Requested image blocks can accompany text, so the complete memory representation cannot be classified as text alone. Page limits account heuristically for images and parallel tool siblings; they do not prove provider acceptance. Path normalization is not a filesystem sandbox. See notes and history tools.

The extension supports continuity and narrow context-budget reflection: usage changes the representation that drives reminders and rollover policy. It does not establish improved task capacity, conjectural learning, or self-improvement. Retention and delivery do not validate saved assertions about progress. Static tests describe content and persistence contracts with faux responses; no retained execution establishes faithful downstream dependence on recalled content. Pinned host inspection and controlled continuation runs would change those limits.

• Exact analysis — see-also: canonical records, supporting quotations and fourteen-axis comparison profile.
• Reflective system — defined-in: the narrow self-representation mapping used here.
• Conjectural learning — defined-in: the stronger learning claim not established by context continuity.