Proposed specificationSource-located exemplarH1

Observer

Notify registered dependents of changes.

JOIN POINTsubject_change_notificationRECORD STATUSCandidate · v0.1.0

UML class view

The proposed contract drawn as participant roles, received calls, and numbered dependencies.

Object interactions

The same roles and calls as a class collaboration and a numbered message sequence.

Object interaction diagram for Observer, showing role collaboration and a numbered message sequence — FIG. C02 / OBJECT INTERACTIONS
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Pointcut

Where the mechanism applies. All four dimensions belong to the proposed match, not just its vocabulary.

Context: A subject changes state or emits lifecycle information.
Trigger: The subject publishes a change notification.
Structure: Subscription registry, event payload, and observer callbacks.
Effect: Currently registered observers are notified under declared ordering semantics.

Protected contract

The obligation that clients, operators, and auditors should be able to rely on.

Requires: Observer identity and subscription lifetime are defined.
Ensures: Notification follows the event and unsubscribed observers no longer receive it.
Invariant: Observer failure does not corrupt subject state.
Violation: Callback errors and cascades are isolated or propagated by explicit policy.

Negative control

Polling the subject rather than notification is not the observer pointcut.

Variation & lifecycle

The hot spot is admitted only where the protected semantics survive.

Permitted variation

Event emitter, listener, hooks, and stream observers.

Test obligation

Test subscribe, unsubscribe, ordering, callback error, and reentrancy.

Evolution question

Did observer callbacks gain event schemas and lifecycle controls?

Prompt + code design

An illustrative prompt and a small design sketch for the proposed contract. Names and APIs are invented; this is not a repository excerpt.

PROMPT SKETCH

Notify subscribers after a subject change, within their declared subscription lifetime. An unsubscribed observer must not receive later notifications.

CODE DESIGN / PYTHON

class Subject:
    def __init__(self):
        self.observers = {}

    def subscribe(self, observer):
        self.observers[observer.id] = observer

    def unsubscribe(self, observer_id):
        self.observers.pop(observer_id, None)

    def publish(self, event):
        for observer in list(self.observers.values()):
            observer.notify(event)

Illustrative design sketch. Subscription lifetime is the contract; notification order is secondary. This example is a teaching aid, not implementation evidence or a conformance claim.

Detection & matching

The frozen rule that retrieves this record, the canonical source exemplar, and the control that should stay unmatched.

Join point: subject_change_notification
Source locator: Sarkar and Sarkar
Lexical cue: (?i)\b(?:Observer|observer|add[_-]?listener|register[_-]?(?:listener|observer))\bFrozen expression, v0.1.0. A match is a retrieval cue, not a confirmed implementation.
Aliases: None
Canonical exemplar: mastra-ai/mastrapackages/core/src/events/event-emitter/index.ts:21Support: packages/core/src/events/unix-socket-pubsub-solo.test.ts:54
Negative control: Polling the subject rather than notification is not the observer pointcut.

Scope-anchored review. pohe-agent analyze <repo> --pattern C02 anchors the cue to its enclosing declaration and checks a separate operational signature for all four pointcut dimensions. Missing roles and negative-control risks remain visible; a structural match is not E2/E3. Calibration report ↗

Repository files

Up to five public files retrieved by the frozen cue and pinned to the audited commit. A match is a place to inspect, not a confirmed implementation.

01mastra-ai/mastrapackages/core/src/events/event-emitter/index.ts:21CANONICAL SOURCE 02aaif-goose/goosecrates/goose-mcp/src/autovisualiser/templates/assets/leaflet.min.js:5RETRIEVAL CUE 03affaan-m/ECCskills/continuous-learning-v2/scripts/instinct-cli.py:307RETRIEVAL CUE 04agno-agi/agnolibs/agno/agno/knowledge/knowledge.py:366RETRIEVAL CUE 05anomalyco/opencodepackages/ai/src/protocols/open-responses-channel.ts:51RETRIEVAL CUE

Evidence & provenance

Each layer answers a different question. Do not substitute retrieval for review.

Source-located exemplar

A concrete source anchor is available for this proposed record. It is one exemplar, not evidence that all repositories—or every contract field—conform.

Review boundary: this candidate and its specification come from an AI-assisted study. Independent human validation remains open.

ANY-EVIDENCE FAMILY COVERAGE29/36

80.6% of repository families in the frozen panel have at least one current cue, historical cue, or canonical source layer. This is not confirmed prevalence.

Current lexical-cue repositories: 32 / 41

Canonical source anchormastra-ai/mastra 899383db98e0packages/core/src/events/event-emitter/index.ts:21

Supporting surfacepackages/core/src/events/unix-socket-pubsub-solo.test.ts:54

Registered subscribers receive event notifications.

Exploratory retrieval cue Regex / v0.1.0

(?i)\b(?:Observer|observer|add[_-]?listener|register[_-]?(?:listener|observer))\b

This expression is a discovery instrument only. A match is a retrieval cue—not a confirmed implementation, pointcut match, or contract proof.