v0.5.2

v0.5.2

PiG 0.5.2 is a bug-fix and Pi-catch-up release. It follows Pi v1.4.0. Install it with go install github.com/MichaelKinsy/PiG/cmd/pig@latest.

PiG is a Go implementation of Pi, the reference. Pi's behavior is the contract, and every place PiG differs is a numbered divergence. PiG is not an official Pi project, and Pi's maintainers have not endorsed it. It was created by Michael Kinsy and originally developed at Hewlett Packard Enterprise.

Thanks

This release has fixes that came straight from your reports and patches 🐷

• @JihongWEI reported #264 (a Node extension kept seeing a session entry the host had refused), #265 (MCP registration was quadratic in the number of tools) and #266 (CodeMode sandbox construction and discovery were quadratic, and discovery ignored cancellation). All three are fixed. Their report on headless MCP (#214) is also answered in this release.
• @liangzhiyu reported #271 and sent #270: two parallel edit calls through two names of one file could lose an edit. Their commit is in the fix with their authorship kept.
• @mblarsen sent #215, which makes ctx.hasPendingMessages() ask the host (their commit is in this release, with their authorship), and reported #267, the /reload stale-context error.
• @ShoichiTect reported #259: prompts failing with "No model selected" after /scoped-models and Ctrl+P.
• @edersohe reported #260, pig --list-models showing different models than Pi. The client half is fixed here; see Known issues for the rest.

Fixes for reported issues

• #259: after /scoped-models refreshed the catalogs and Ctrl+P switched models, prompts failed with "No model selected". The scope now holds the Session's runtime-bound models, as Pi's selector does.
• #260 (client half): pig --list-models prints only the models the runtime reports as available, as Pi does. It used to add every bundled model of each provider with a key, so models a refreshed catalog had dropped came back. The hosted half of #260 is not part of this release.
• #264: a Node extension no longer sees an appended entry the host refused (#272).
• #265, #266: MCP registration, CodeMode sandbox construction and tool discovery are linear in the number of tools. For a 100,000-tool catalog, sandbox construction went from 22.4 s to 40 ms and MCP registration after the last page from 53.2 s to 2.45 s on the reporter's repro programs (#268). Discovery stops when its context is cancelled.
• #267: /reload no longer reports Extension "builtin:codemode" error: This extension ctx is stale after session replacement or reload. (#286).
• #271: parallel edit calls through a hard link or a case alias of one file are ordered, so neither edit is lost (#284, building on #270). Pi has the same lost edit for hard links, so this goes beyond Pi on purpose: divergence D190.
• #215: ctx.hasPendingMessages() reports a steering or follow-up message queued while a handler is awaited, as Pi's live getter does.
• #245: opening a Durable store written by pi-durable 1.3.0 no longer leaves you unable to go back to it. PiG writes schema version 2, which no Pi release reads yet, so it first copies an older store to <path>.schema-<N>.bak. Divergence D188 (#256).

Pi catch-up

• Pi 1.4.0, including client identity (User-Agent and provider attribution), Rex terminal support (hyperlinks, true color, Kitty images), PI_CODEMODE_MAX_WORKERS and waiting for a free codemode worker, MiniMax-M3.1-Flash, gpt-6.1-sol as the default GitHub Copilot model, HTTP 413 treated as context overflow, the retry classifier fixes, @ autocomplete with regex characters, /compact <instructions> on a split turn, extension tools after resume and /tree, concurrent extension dialogs, terminal-mode restore on abnormal exit, unclosed $$ math and tables, CJK Markdown emphasis, UTF-8 BOM in mcp.json.
• grep runs rg --no-config as Pi does, and a session recovered from a response cut off at the output limit omits the tool results of the truncated call (Pi 8c4e8738 and 02726086).
• Image input for System One classifiers (Pi 7f225f25): codemode models.classify() accepts images for the classifier models Pi 1.4.0 lists (Jev on typesafe and cloudflare-workers-ai, Clef on cloudflare-workers-ai, OpenRouter decision models whose catalog lists image input), with the compat fields imageInput and sendImageOptInHeader.
• Divergences retired because Pi changed: D126 and D171.

Extension SDKs

• Go, Python and Rust extensions can create child agent sessions (createAgentSession), construct SessionManager, SettingsManager and ModelRuntime, override a built-in tool and delegate to it, and use Pi's pi-ai helpers and pi-tui helpers. pi.exec honors an abort signal in every SDK.
• Dialogs return the JSON value the client answered with, as Pi's do. This changes return types in Go, Python and Rust (see Upgrading).
• Extension tool calls of one parallel batch, and timer callbacks, reach the host and RPC clients in Pi's order. The wire field that carries this is recorded as D189 in docs/additive-features.md.
• A per-SDK ledger of every runtime export Pi serves to extensions is checked in CI (docs/extension-sdk-exports.md).

Durable and Chord

• Durable: a crash-loop guard (a task cut off five times in a row without committing is parked, HarnessSettings.RestartLimit), richer OnReport information, HarnessSettings.AfterFailedRun, and telemetry spans and metrics from Pi's telemetry commits.
• Chord link protocol version 4, with the host API changes listed under Upgrading.
• Many concurrency fixes found by stress runs under the race detector (host manager, chord links, cache locks on file systems without locks, fork from file, packed cells).

Size and speed

Numbers below are the ones recorded in the changelog fragments, each from its own measurement.

• The root module go install downloads is about 184 MB, under the 185 MB budget that keeps it well inside Go's 500 MB limit.
• The pig binary is 3.7 MB smaller (linux/amd64: 70,348,960 to 66,601,120 bytes).
• Interactive sessions start with less memory (syntax grammars decode on first use), and idle sessions hold less.
• RPC and JSON mode, long sessions, and Anthropic and OpenAI Completions request building use less CPU per turn. Fragments give per-change figures.

Upgrading

Breaking changes for Go code and the SDKs (each has a before and after in the CHANGELOG):

• chord/host: CreateHost needs Self; Connect takes ConnectOptions; Host.Get waits until ready (Host.Hold is the old behavior); GetOptions.At is gone.
• chord/output is a new package; the output buffer types moved there from durable/harness.
• durable/storage/sqlite: Options is SqliteStorageOptions; the Node options split into NodeSqliteDatabaseOptions.
• ai: TelemetryContext is Telemetry; ai.PiUserAgent is gone (use ai.FormatUserAgent).
• Go SDK: dialog methods return any values; ModelRegistry.Find returns an error; sdk.ReadonlySessionManager replaces sdk.SessionManager as the type of ctx.SessionManager(). Rust: ModelRegistry::find returns io::Result<Option<Value>>; before_agent_start takes a typed event. pig extension upgrade rewrites what has one safe form and lists the rest.
• agent.SettleGate and extension.CallLane are removed from the public API.
• A Durable task cut off five times in a row is parked; set RestartLimit to +Inf to keep the old behavior.

Security

Two security events landed on 2026-10-20 and 2026-10-21, and this release answers both.

Update your own Node.js. Node.js published security releases on 2026-10-21 (22.23.4, 24.22.1 and 26.12.1). The four high severity issues are CVE-2026-105482 (dns.resolve truncates names that contain a NUL), CVE-2026-105483 and CVE-2026-106069 (TLS certificate hostname checks bypassed with fullwidth-digit and loosely resolving IP addresses) and CVE-2026-111497 (Brotli decoder out-of-bounds write that permits remote code execution). The advisory lists the medium and low issues too: https://nodejs.org/en/blog/vulnerability/october-2026-security-releases. PiG embeds no Node.js binary, so nothing in PiG's own build changes for you. The Node.js that runs your TypeScript and JavaScript extensions is the one you installed, so update it to 22.23.4, 24.22.1, 26.12.1 or later. PiG's CI, parity image and devcontainer moved to 24.22.1 (current 26.12.1).

eMudhra and emSign certificate authorities (D191). The private keys of eight eMudhra intermediate CAs can be recovered from their public certificates (Mozilla bug 2083449). Sectigo cross-signed the same keys, so some systems still trust chains through them, and Go clients check neither revocation nor Certificate Transparency. Mozilla also removed three emSign roots from NSS 3.131.1 (emSign ECC Root CA - G3, emSign Root CA - C1 and emSign ECC Root CA - C3). PiG's own TLS connections now refuse a chain through any of the eight intermediates (by public key, so the cross-signed paths are refused too) or any of the three roots. That covers model providers, OAuth, MCP, package and tool downloads, self-update, the Codex WebSocket and Bedrock, and the error names the CA. Go 1.27.3 already distrusts the eight intermediates. D191 adds the three roots, covers builds with an older Go (go.mod says go 1.26.0), and gives the clear error. D191 is an additive record in docs/additive-features.md, not a divergence from Pi. TLS that an extension process opens itself (Node, Python, Rust) is outside this check; for Node, the update above covers it.

Node.js 24.22.1 changes the microtask order of values().next() after a buffered byte-stream read, as Node 26.7.0 does. See Known issues.

Known issues

• PiG's Web Streams microtask models and goldens (ai/testdata/node-microtasks) record Node 24.19.0 (oracle-node-version). Node 24.22.1, which CI now runs, orders one case differently (values-buffered/bytes); the live comparison is skipped on it. Moving the models to the new order is separate work.
• Three Windows-only test failures (a Python test fixture's line endings, a Windows Pi comparison for OpenAI responses, and a conformance package timeout) are fixed after the release on main. They are tests only and change nothing you install.
• #260 is not closed: the model catalog route on pi-in-go.dev is hosted outside this repository.

Full changelog

See CHANGELOG.md (0.5.2 section). Thanks also to @sam-phinizy for #222, the v0.5.0 module zip report that 0.5.1 fixed.