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Changelog

All notable changes to STELLA are documented here. For the full changelog, see CHANGELOG.md on GitHub.

The format follows Keep a Changelog, and STELLA uses Semantic Versioning.

Version Policy​

  • Major (X.0.0): Breaking changes to APIs or configuration
  • Minor (0.X.0): New features, backward compatible
  • Patch (0.0.X): Bug fixes, backward compatible

[Unreleased]​

Added​

Open source & project governance

  • STELLA is now released under the MIT License (© Universität St. Gallen (HSG) & University of Zurich (UZH)) — free to use, modify, and self-host
  • Public documentation and a researcher-focused landing page are now hosted on GitHub Pages at c4dhi.github.io/STELLA, auto-deployed from main
  • Community & release files added to the repository: CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md (private vulnerability reporting), NOTICE.md (third-party attributions), CITATION.cff (GitHub "Cite this repository"), and RELEASING.md

Backup, restore & relocation (#378)

  • Full-system export/import for backups and machine-to-machine migration, driven by a guided wizard (./scripts/start-k8s.sh --backup) with a readable restore report
  • STELLA_DATA_ROOT relocates all heavy storage (PVCs, models, temp) onto a chosen disk

Voice — TTS providers & voices

  • Multiple text-to-speech providers: Piper (default local), in-process Qwen3-TTS, ChatterBox multilingual (EN/DE), and Voxtral (opt-in, GPU) with low-VRAM 4-bit/8-bit knobs
  • Default Stella voice registry shipped with de + en reference clips, plus language-aware, per-agent and per-stream reference-voice selection

Language handling

  • End-to-end language support: STT acoustic language detection, coherent per-turn language resolution moved into the SDK and adopted by both agents, and a configurable resolver with sensible defaults

Barge-in

  • Users can interrupt the agent mid-speech (voice and text), reusing the voice plumbing, via a configurable COMMIT/RESUME evaluator — at parity across stella-v2 and stella-light

Setup wizard & deployment

  • Chapter-based onboarding wizard: auto-generates required secrets, guides the LiveKit internal URL with same-machine IP detection, prompts for STELLA_DATA_ROOT and a Hugging Face token, and adds a skippable initial-admin bootstrap chapter
  • Independently configurable public frontend and backend URLs; manifest-driven runtime-variable palette with a minimum config-compiler version; env-var templates and pipeline configs scoped to agent type + version

Sessions & transcripts

  • Sessions auto-end on inactivity or max-duration
  • Transcript download with a mode selector (transcript / + verdicts / full debug export) and per-message-type checkboxes
  • Word-by-word speech highlighting (teleprompter) on both chat surfaces

Agent Configurator — Expert Module

  • Deterministic, literature-informed verdict responses: each expert verdict maps to an action (inform/prepend/override/short_circuit) + template, applied by priority in the arbitration layer so safety-critical output doesn't depend on the LLM's interpretation
  • Generic, editable verdict labels with LLM-facing explanations (label + explanation handed to the classifier; action stays in arbitration); fixed output interface
  • Agent-declared expert defaults published from config/experts/*.json to AgentType.expertDefaults, capability-gated (task_extraction ← plans, assessment pool ← experts)
  • Unified prompt editor in the New Custom Expert form (#178), Always-Triggered toggle on creation (#175), and an unsaved-changes discard guard on close (#177)

Stella Light

  • Barge-in support at parity with stella-v2: a configurable Barge-in Evaluator (COMMIT/RESUME classifier) with an editable prompt/model in the Configurator, plus BARGE_IN_ENABLED / BARGE_IN_EVAL_TIMEOUT_MS env controls
  • "Branch chosen" indicator now renders for the light agent too — it tracks state changes and emits last_transition, reaching parity with stella-v2

Agent SDK — shared progress builder (#310)

  • New stella_agent_sdk.progress.progress_from_full_state() — the single canonical get_full_state() → ProgressState transform every agent uses, replacing two hand-maintained per-agent copies that had drifted (the source of the disappearing-skipped-state and 8000% bugs). Group status derives only from the authoritative state.status; the percentage is used raw (0–100); real task.status, goal metadata, and discovered insights are handled consistently
  • New build_last_transition() — shared "branch chosen" derivation; agent identity is parameterized via extra_metadata and the clock is injectable for deterministic tests
  • Additive and backward compatible: existing custom agents need no changes. See Progress Tracking → State machine–backed progress

Changed​

Editable agent prompts

  • stella-v2: response and bridge behavioral prose moved into editable prompt slots behind one unified template interface; the bridge now streams to TTS and carries the full reaction to cover the response gap; sharper per-expert engage/tap-out contracts
  • stella-light: persona + conversation guidelines merged into a single editable System Prompt; safety guardrails and phase-transition notes moved into editable slots; deliverable-driven steering with precise skip semantics

State machine — task completion (#291)

  • Task completion is now derived from collected data: a task with deliverables is addressed automatically once its required deliverables are collected (or, for an all-optional task, once every declared deliverable is in), with no separate "mark complete" step. Deliverable-less tasks still require an explicit complete/skip. A state advances only once every task (required and optional) is addressed, and is never vacuously complete on entry.

Removed​

stella-v2 — Input Gate (#363)

  • Removed the Input Gate stage from the stella-v2 pipeline — experts now self-gate and arbitration filters, simplifying the pipeline to five stages

Fixed​

Audio & deployment reliability

  • Prevent the STT stall when an audio track ends or the participant mutes; audio-output readiness is now a real-time round-trip test
  • LiveKit audio and webhook-processing fixes; barge-in now silences client audio on interrupt with a hardened evaluator
  • Agent image caching now rebuilds when Docker/config changes so config edits actually take effect

Progress / to-do rendering (#291)

  • A skipped task no longer renders as pending — it shows as skipped and counts toward "tasks done". Skipping a task now also marks its uncollected deliverables skipped.
  • stella-v2: skipping a task no longer makes the whole state disappear from the route view (group status now follows the state machine's authoritative status), and the progress percentage is no longer mis-scaled.
  • Live and historical-replay views now share one progress→to-do conversion, so they can't disagree about task status.
  • (#310) The full_state → progress transform is now consolidated into one shared SDK builder, so the agents can no longer drift; the two historical bugs above are now covered by a single golden-fixture suite.

Goal states (#310)

  • Goal-level deliverables now honour the skip cascade, same as regular task deliverables: once a goal state completes, any uncollected goal deliverable renders skipped instead of a stale pending, and the synthetic goal task reads completed.

[0.3.0] - 2026-01-29​

Added​

Participant Experience

  • Text-only interface for participant screen (#24)
  • Marketing landing page (#12)
  • Mobile-ready participant screen with responsive design (#25)
  • Session transcript export functionality (#50)
  • Public web interface for interviewees (#3)

Agent & System Capabilities

  • Agent Toolkit/Toolbox implementation for extensible agent capabilities (#20)
  • Enhanced Conversational Agent with improved dialogue handling (#88)
  • Whisper integration for Text-to-Speech (#7)
  • Public Projects feature for shared access (#4)
  • Environment variable override support in DeployAgentModal

Project & User Management

  • Per-user project basis with sharing capabilities (#34)
  • Environment Variable Templates for Agent Types (#28)
  • System-wide state persistence (#31)

Documentation & Onboarding

  • Adaptive documentation system (#29)
  • Dynamic onboarding through start-script (#56)
  • Custom Tools guide for extending agent capabilities
  • Database Schema documentation with complete Prisma model reference
  • Custom Agent Visualizers guide for creating face visualizers
  • Environment Variables reference documentation
  • Message Recording deployment guide
  • Authentication guide with JWT implementation details

Changed​

  • Refactored Conversational AI Agent to SDK architecture (#10)
  • Migrated system from Minikube to K3S with enforced microservice architecture for STT and TTS (#14)
  • Improved start script and repository structure (#16)
  • Improved code block styling with automatic word wrapping
  • Updated architecture overview with database references
  • Enhanced cross-linking between documentation pages

Fixed​

  • Fixed Whisper warmup functions not existing (#70)
  • Fixed Whisper not reliably transcribing speech (#49) [P0]
  • Fixed double texting issue (#9)
  • Fixed new user error when no projects exist (#36)
  • Fixed initial message bug (#6)
  • Fixed unselecting Debug in Session Overview not working (#11)
  • Fixed environment variables not reaching agent pods when modified in deploy modal
  • Fixed LiveKit Production page title formatting

[0.2.0] - 2026-01-17​

Added​

  • Complete documentation site with Docusaurus
  • Getting Started guides (Quick Start, Installation, First Agent)
  • Architecture documentation (Overview, Data Flow, Session Lifecycle, Kubernetes)
  • SDK Reference (Overview, Base Agent, Plans, Tools, Streaming, TypeScript Types)
  • Deployment guides (Kubernetes, Production, Production Checklist)
  • LiveKit integration documentation
  • Contributing guidelines (Development Setup, Coding Standards, PR Process)
  • Plan Structure documentation with state machine details

Changed​

  • Migrated documentation from standalone markdown files to Docusaurus
  • Reorganized documentation structure for better navigation

[0.1.0] - 2026-01-10​

Added​

  • Initial STELLA backend release
  • NestJS-based session management server
  • LiveKit integration for real-time audio/video
  • PostgreSQL database with Prisma ORM
  • Kubernetes orchestration for agent pods
  • STELLA Agent SDK for Python agents
  • State machine for conversation flow management
  • React frontend with visualizer gallery
  • JWT-based authentication system
  • Project and session management APIs

Upgrade Guides​

When upgrading between versions, check for:

  1. Breaking Changes: Listed under each version's "Changed" or "Removed" sections
  2. Database Migrations: Run npx prisma migrate deploy after updating
  3. Configuration Changes: Compare your .env with .env.example
  4. SDK Updates: Update agent dependencies to match backend version

Documentation Versions​

This documentation supports versioning. Use the version dropdown in the navbar to access documentation for older releases. The "Next" version contains unreleased changes from the main branch.