Architecture

Pi Sych is deliberately a small mechanical layer: it tracks paths and hashes, launches bounded workers, exposes read-only literature lookup, and preserves explicit human review. Skills and humans own semantic judgment.

Supervisor contract

The supervisor sees three Pi Sych tools:

• project_status checks or acknowledges mechanical project state;
• dispatch_worker runs one short-lived worker with clean or trajectory context; and
• literature_search performs read-only lookup in the configured local literature index.

At supervisor start Pi Sych adds concise supervisor guidance and, when present, configured project agents instructions and the worker model catalog. Pi itself describes active tools and native MCP servers; Pi Sych does not reproduce those inventories. The supervisor guidance uses two independent task-posture dimensions:

• persistence — once the requested outcome and authorization boundary are clear, continue until completion or a genuine blocker rather than stopping merely to ask whether to continue; and
• scrutiny — increase checking for authored prose, consequential project-state decisions, release/publication work, external side effects, and ambiguous intent.

High scrutiny does not itself require another user checkpoint. A clear request to review, rewrite, implement, or complete a defined scope is authorization for that scope. A new checkpoint is needed when the work would cross into a new consequential choice, side effect, or material ambiguity not already covered by the user’s instruction or accepted project state.

Direct work and delegation

There is no universal direct-work or worker default. The supervisor chooses by task and context.

Direct work is efficient for simple or tightly connected work. Dispatch is useful for independent context, breadth, specialization, cheaper execution, independent review, or substantial bounded work. Context need is separate from delegation choice:

• a clean worker receives no supervisor transcript and should be used when the explicit packet is sufficient;
• a trajectory worker receives Pi’s persisted supervisor branch ending immediately before the dispatching assistant entry and should be used when prior conversation materially helps; and
• supervisor pre-work can convert conversational context into explicit state such as a plan, TODO, brief, or context file, allowing later clean delegation.

Needing prior context therefore does not imply that the supervisor must execute the task itself. The project skill’s delegation module teaches optional pre-walk, planner/builder, orchestrator, exploration, and independent-review patterns using these dispatch choices. These are semantic working possibilities, not runtime workflows or automatic model swaps. Explorer summaries remain interpretations; decisive source material should remain available to the model making the decision.

Before dispatch, the supervisor inspects the available skill catalogue, selects only useful skills, and supplies one explicit assignment, expected output, capability mode, context files, context mode, model role, thinking level when useful, and bounded timeout. Configured agents files are automatically included when present. Optional workerInstructions supplies worker-specific guidance through Pi’s native AGENTS context-file discovery, not the assignment prompt. For that dispatch only, Pi Sych creates a private temporary worker agent directory containing the configured agent files and a launch-scoped AGENTS.override.md that preserves existing worker instructions before the supplied guidance. Pi then loads project/ancestor AGENTS files by its normal discovery and precedence. Omission uses the configured worker agent directory unchanged, injects no instructions, and disables context-file discovery for that worker. For a writing worker, the package skills/write/DEFAULT_STYLE.md is included as a baseline and a project STYLE.md, when present, is included as a local override. These style files are not loaded for unrelated work. Worker modes control visible Pi tools; they are not sandboxes.

Worker lifecycle

A worker is a separate short-lived Pi process with one immutable terminal result. It reads its explicit assignment, every context file and selected skill, then the routed methods/modules. Trajectory history is background, not a source of additional assignments or approval. The dispatch_worker call renderer shows a prioritized human-readable summary when collapsed and labeled assignment, execution, and context details when expanded; live activity lines include available tool argument details in bounded readable form.

Ordinary workers do not receive MCP or codemode. remoteResearch: true explicitly loads Pi’s builtin:mcp and builtin:codemode extensions; the worker reads its own mcp.json from its agent directory. Users configure and authenticate that file with native Pi MCP commands. The supervisor’s MCP configuration and companion extensions are not copied to workers. Pi’s CLI --tools allowlist filters dynamically discovered MCP tools out of codemode’s nested tool set, so the worker extension applies the task’s selected Pi tool set at session start instead. Pi’s per-server and per-tool MCP exposure still follows the worker’s native mcp.json (codemode is the default). Tool availability does not guarantee credentials or access.

The worker reports complete, partial, or failed, a non-empty summary, existing project-relative output files, and limitations. A worker’s complete status is not human approval. Cancellation, timeout, spawn failure, a signal exit, or non-zero exit takes precedence over a result file. On Pi versions that expose agent_settled.aborted in JSON output, an explicit true also classifies an otherwise normally exited worker as cancelled rather than accepting its submitted result as success. A structurally valid report recovered after interruption or process failure is retained separately as interruptedReport, with an explicit warning that work may be incomplete or inaccurate. Its claimed status, summary, limitations, and reported paths are provisional; paths may no longer exist. The primary error remains, and result is absent. Missing or invalid reports do not mask the interruption. Missing or false settlement flags do not establish success; process checks and result validation remain required. Before launch and after termination, Pi Sych snapshots project files and reports reported, observed, and unexpected changed paths independently of worker success. Observation does not undo changes. Temporary runtime/session state is removed after every outcome. Signal exits retain their terminating signal in the failure diagnostic. Git snapshot fallback covers file enumeration, not file-hashing errors; observation failures remain explicit instead of switching snapshot scope. On POSIX, workers have their own process group. Timeout or cancellation starts graceful group termination, with ten seconds before forced cleanup. A normally exited worker also gets ten seconds to drain inherited output pipes, without being reclassified as timed out. Windows signals the direct child; pipe cleanup still prevents descendants from holding dispatch open.

Project state

SYNC.json version 2 records tracked file hashes and dependency paths. project_status reports missing files, changed hashes, persisted status, project-brief problems, and dependency impact. A changed hash proves only changed content. Acknowledgement records reviewed state, not correctness or semantic authority. Acknowledgement holds an exclusive SYNC.json.lock across its read–modify–write transaction. Concurrent calls fail explicitly and can be retried; a lock left by a crash must be removed only after confirming no acknowledgement is running. This coordinates Pi Sych acknowledgements, not arbitrary external editors.

Configuration and compaction

Pi Sych configuration layers the global <pi-config-root>/pi-sych/config.json with the project .pi/pi-sych/config.json; project keys override matching global keys, including individual nested compaction fields. Unknown keys are rejected. The small v2 configuration owns custom compaction policy, an optional completion reassessment, and the local literature database path, not native Pi settings.

Custom compaction uses the active supervisor model and runs for configured manual/native compaction requests when enabled. Proactive admission occurs at agent_settled when context usage reaches the configured threshold (default 150,000 tokens), the context window can reach that threshold, the agent is idle, no messages are pending, and no compaction is already in flight. The threshold is independent of Pi’s reserve-token settings.

Optional completion reassessment defaults off. When enabled, the workbench uses Pi’s final actionable agent_before_settle event after ordinary post-run handling. It injects one hidden message and requests one continuation only for a completed outcome, with no queued messages and context.canContinue true. A per-user-message guard prevents recursive reassessment; a new user message resets it. The instruction keeps work within existing authorization and directs the supervisor to stop when complete or genuinely blocked. This trigger is separate from compaction.

The continuation is a bounded observable trajectory: objective, authorization, constraints, progress, decisions, inferences, failed or rejected paths, unresolved issues, active work, next action, files, and project-state gaps. It uses bounded observable messages, bounded retained tail, and bounded canonical snapshots. Recorded user-explicit and accepted-project decision attributions are preserved without verification; inferences are kept separate. Malformed optional collections and invalid individual members are skipped independently so usable siblings survive. Invalid promotion candidates are likewise skipped rather than invalidating the memory summary. The required objective and next action must remain usable; malformed JSON or missing or unusable required fields leave native fallback in control.

At most bounded one-line proposals are appended to the configured inbox as visibly unreviewed state. Canonical semantic files are never mutated. Inbox safety or append failures skip proposals without discarding otherwise usable memory; an unreadable existing inbox count is reported as unavailable, not zero. Cancellation during inbox safety or directory operations is checked before append, preventing late proposal writes. If custom compaction is disabled, omitted, fails, is cancelled, or lacks usable required summary fields, Pi’s native compactor remains in control.

Local literature

literature_search queries the configured read-only SQLite FTS5 index. It returns compact readable results and matching structured data for nested callers, including nullable metadata, snippets, scores and source paths. Results support discovery and provenance, not source verification or completeness. Exact claims still require inspection of the underlying source when material. The configured database may be absolute or relative; relative global paths resolve from the global Pi Sych config directory, and relative project overrides from the project root.

The research skill is capability-aware at the guidance layer. It tells the model to inspect what is actually available and choose by function: local corpus discovery, scholarly metadata/graph lookup, focused scholarly retrieval, PDF/full-text inspection, broad discovery search, or targeted fetch/browser verification. Tool outputs should refine later retrieval rather than be called mechanically.

Skills and supporting guidance

Seven umbrella skills are public: project, write, analyze, code, review, research, and automation. Each uses bounded task routes with primary guidance and optional overlays. Shared methods under skills/_methods provide reusable procedures; local modules adapt them to a genre, artifact, or task.

Writing and review guidance treats standalone artifact self-containment as a quality criterion. Process residue, unexplained version/revision language, reviewer-response wording, and unmotivated denials or contrasts are potential context leakage when they have no reader-visible job. Review lenses trace paragraph and sentence flow in reading order, and examine cumulative habits such as semicolon/em-dash repetition, serial “not X but Y” turns, and stacked hedges. These are diagnostic prompts, not counts or bans: preserve useful idiosyncrasy, purposeful constructions, and calibrated uncertainty, while explaining concrete reader effects and offering minimal repairs. Response letters and revision memos may appropriately discuss reviewers, versions, and changes because the revision process is part of their subject.

The prompt hierarchy is intentionally layered: always-visible tool/supervisor text carries salient posture and boundaries, umbrella skills route the task, and routed methods/modules carry detail. Routes are ordinary Markdown links, not a workflow engine or prompt inheritance mechanism.

automation is semantic guidance, not a new orchestration runtime. Five thin packaged review prompts select a lens and defer substantive procedure to the review skill. An optional user-maintained STACK.md may describe durable computer/environment facts for computer-use work; automation guidance consults it when available, while runtime state remains the authority for what can be used now.

Guidance growth and review provenance

The runtime intentionally stays narrower than the guidance catalogue. Seven public SKILL.md entry points route task-specific work to specialist modules/ and reusable skills/_methods/. Adding a specialist recipe or example does not add a new public skill, persistent agent, runtime tool, or mandatory workflow stage. Load only the guidance needed for the task; avoid copying shared policy into every prompt, module, or repository instruction file.

Review is a useful example of this separation. Packaged prompts/review-*.md choose optional lenses, but the skills/review/SKILL.md contract also applies when a user requests a review without a preset prompt. Reviews returned by workers or invoked through packaged prompts end with a brief LLM review line explaining how the requested lens may shape the findings—for example, adversarial fault-finding may surface less relevant objections, while a collaborative lens may miss flaws needing a more skeptical pass. This is a useful interpretive cue, not a generic disclaimer or list of unchecked work.

The supervisor evaluates those observations against accepted project state and evidence. Author-authored Plannotator notes express author intent; co-author and human peer-review comments warrant serious collaborative treatment. Independent LLM reports remain advisory even when generated by a clean-context worker. Material errors require attention regardless of who noticed them, but iterative LLM objections are not a mandate to endlessly weaken a defensible manuscript. Neither review provenance nor editorial authority is assigned by the TypeScript worker-result schema.

Optional integrations

Pi owns MCP transport, server discovery, authentication and /mcp; use /mcp or pi mcp list, pi mcp login, and pi mcp logout rather than a Pi Sych MCP wrapper. Plannotator remains a separately loadable narrow human-review adapter. Independently installed document, web and browser tools can satisfy capability needs without runtime coupling to Pi Sych. None of these mechanisms silently promotes model output into accepted project state.