💡 Platform feature: script-interop-bus (lightweight cross-script event bridge for composable automation pipelines)

[github-actions[bot]]

Summary

A shared, lightweight event bus mechanism (using ScriptProperties or a dedicated Sheet) that allows deployed scripts to chain together — for example, gmail-ai-classifier classifies an email, emits an event, and gmail-to-drive-by-labels automatically archives it. Transforms the script catalog from isolated tools into composable pipelines, positioning the project as a free, local-first alternative to Workspace Studio for multi-step automation.

Market Signal

Google Workspace Studio (rolling out through 2026) promotes composable, agentic workflows with visual chaining of automation steps. The market is decisively moving from single-purpose automations to orchestrated pipelines — Zapier, Make, and n8n all center on multi-step workflow composition as their core value proposition. However, Studio requires Business/Enterprise Workspace plans with limited automation runs per plan tier. A free, native-GAS interop bus fills the gap for personal and small-team users who can't or won't pay for Studio. The September 2026 Workspace Studio announcement adding Drive/Gmail/Chat automation steps confirms Google's all-in bet on composability.

User Signal

PR #530 (tag-based retention and 2-way rules sync engine, merged September 2, size XXL) proves the need already exists — it implements a form of cross-script communication between gmail-ai-classifier and gmail-retention-policy. This is the project's largest recent PR and its most architecturally significant: it bridges two scripts that previously ran in isolation. As the catalog grows (5 scripts shipping, 34 more proposed), the value of composability grows quadratically. Users deploying 3+ scripts currently manage 3+ independent hourly triggers with no coordination between them.

Technical Opportunity

GAS PropertiesService provides a natural key-value store for event passing between scripts within the same Google account. The existing schedule-in-config pattern (hourly trigger → shouldRunNow() check) can be extended to also check an event queue before/after the main processing loop. Each script remains independently deployable and fully functional — the event bus is opt-in. The shared src/gas-utils.js module is the natural home for bus helper functions (emitEvent(), consumeEvents(), peekEvents()). Events are fire-and-forget metadata, not blocking RPC calls — no execution time overhead beyond a single PropertiesService.getScriptProperties().getProperty() call per trigger run.

Assessment

Dimension	Score	Rationale
Feasibility	high	PropertiesService already used (e.g., shouldRunNow tracks last-run timestamps); event schema is simple JSON; no new APIs required
Impact	high	Unlocks multi-script composition for every catalog entry; formalizes what PR #530 already does ad-hoc; positions project against Studio
Urgency	med	PR #530 proves the need is immediate; but existing scripts work independently, so urgency is about architecture, not user-facing breakage

Adversarial Review

Strongest objection: Adding inter-script coupling creates failure cascades and debugging complexity. Scripts currently have zero dependencies on each other, which is a feature, not a bug. Users may not deploy enough scripts to benefit from composition.

Rebuttal: The bus is strictly opt-in and fire-and-forget: scripts work standalone by default, and the event bus adds zero behavior changes unless explicitly configured. Events are lightweight metadata (JSON in ScriptProperties), not blocking RPC calls — a failed consumer doesn't affect the producer. PR #530's 2-way rules sync already implements cross-script state sharing, proving both the pattern and the demand. The bus formalizes what's already happening organically, replacing ad-hoc integration points with a single, inspectable event log. Debugging is simplified, not complicated, because event flow is visible in one place rather than scattered across script-specific properties.

Suggested Next Step

Design the event bus contract: event schema ({type, source_script, timestamp, payload}), storage mechanism (ScriptProperties vs. shared Sheet — trade-offs around quota limits and inspectability), and discovery protocol. Implement a proof-of-concept with gmail-ai-classifier emitting email-classified events and gmail-to-drive-by-labels consuming them on its next hourly run. Add bus helper functions to src/gas-utils.js with full Jest test coverage.