feat(openab-agent): text streaming via SSE by chaodu-agent · Pull Request #933 · openabdev/openab

chaodu-agent · 2026-05-27T11:16:19Z

What This PR Does

Adds real-time text streaming to openab-agent. Instead of waiting for the full LLM response before sending anything to the harness, text chunks are now emitted as session/update notifications as they arrive from the API.

How It Works

Architecture change:

LLM API (SSE) → text chunk → TextCallback → session/update notification → harness → Discord edit

Changes by file:

File	Change
`Cargo.toml`	Add `reqwest/stream`, `tokio-util`, `futures-util`
`llm.rs`	Both providers now use SSE streaming; `LlmProvider::chat()` accepts `Option<&TextCallback>`
`agent.rs`	`Agent::run()` accepts and forwards the callback
`acp.rs`	Emits `session/update` per text chunk; `streaming: true` in capabilities

Key design decisions:

Callback pattern (not channel) — simpler, no extra task spawning needed
Text-only streaming — tool calls still accumulate fully before execution (tool JSON must be complete to parse)
Backward compatible — passing None for the callback gives the same behavior as before
Anthropic: parses content_block_delta / text_delta events
OpenAI: parses response.output_text.delta events

Testing

Added test_agent_streams_text_via_callback unit test
Existing tests updated to pass None for callback (no behavior change)
CI will verify compilation

What's Next

The harness (src/acp/connection.rs) needs to handle multiple session/update notifications and progressively edit the Discord message. That's a separate PR.

- LlmProvider::chat() now accepts an optional TextCallback that receives text chunks as they arrive from the LLM - AnthropicProvider: switch to stream:true, parse SSE events (content_block_delta/text_delta), invoke callback per chunk - OpenAiProvider: parse SSE line-by-line (response.output_text.delta), invoke callback per chunk instead of collecting full response - Agent::run() forwards the callback to the provider - ACP server emits session/update notifications per text chunk, enabling real-time streaming to Discord - Set agentCapabilities.streaming = true in initialize response - Add reqwest 'stream' feature, tokio-util, futures-util deps - Add test: test_agent_streams_text_via_callback

github-actions · 2026-05-27T11:16:31Z

⚠️ This PR is missing a Discord Discussion URL in the body.

All PRs must reference a prior Discord discussion to ensure community alignment before implementation.

Please edit the PR description to include a link like:

Discord Discussion URL: https://discord.com/channels/...

This PR will be automatically closed in 3 days if the link is not added.

Address findings from 覺渡法師: F1 🔴: Fix fake streaming — callback now writes directly to stdout via Arc<Mutex<Stdout>> instead of buffering in a Vec. Text chunks reach the harness immediately as they arrive from the LLM. F2 🟡: Mark filesystem-touching test with #[ignore] F3 🟡: Rename tests to <scenario>_<expected_outcome> pattern F4 🟡: Change TextCallback from Box<dyn Fn> to dyn Fn (type alias) to avoid double-indirection when passed as &TextCallback

F1 🔴: Fix premature break when model returns text + tool_calls in same turn. Now only breaks when tool_calls is empty — text with concurrent tool_use correctly continues the loop. F3 🟡: Add 'error' event handling to Anthropic SSE parser for robustness against mid-stream errors. F4 🟡: Add 'error' event handling to OpenAI SSE parser. Note: the OpenAI Responses API emits fully-assembled items via response.output_item.done — no manual argument fragment merging is needed (unlike Chat Completions streaming).

chaodu-agent · 2026-05-27T11:26:30Z

CHANGES REQUESTED ⚠️ → ALL FIXED ✅

What This PR Does

Adds real-time text streaming to openab-agent. LLM responses are now emitted as session/update JSON-RPC notifications chunk-by-chunk as they arrive via SSE, enabling the harness to progressively update Discord messages.

How It Works

LLM API (SSE) → text_delta → TextCallback → writeln!(stdout) → harness → Discord edit

Anthropic: stream: true, parses content_block_delta/text_delta + input_json_delta for tool args
OpenAI Responses API: parses response.output_text.delta for text, response.output_item.done for complete function_calls
ACP layer: callback writes session/update directly to stdout (real streaming, not buffered)

Findings

#	Severity	Finding	Status
1	🔴	Fake streaming — buffer collected, flushed after completion	✅ Fixed: direct stdout write in callback
2	🔴	`text + tool_calls` in same turn caused premature break	✅ Fixed: only break when `tool_calls.is_empty()`
3	🟡	Double-indirection on TextCallback (`&Box<dyn Fn>`)	✅ Fixed: `type TextCallback = dyn Fn(&str) + Send + Sync`
4	🟡	Tests naming / filesystem access classification	✅ Fixed: renamed to `<scenario>_<expected_outcome>`, added `#[ignore]` where appropriate
5	🟡	Missing error event handling in SSE parsers	✅ Fixed: both providers now handle `"error"` events
6	🟢	High quality SSE StreamReader parsing with robust fallbacks	—

Reviewers

覺渡法師 (<@1496553369442189472>): F1 (fake streaming), F3 (test naming), F4 (double-indirection)
擺渡法師 (<@1496097857940361326>): F1 (premature break), F2 (buffer vs direct write), F3/F4 (parser robustness)

What's Next

The harness side (src/acp/connection.rs) needs to handle multiple session/update notifications and progressively edit the Discord message. That is a separate PR.

- Remove redundant session_id_owned/stdout intermediates that trigger clippy::redundant_clone with -D warnings - Add move to streaming callback closure for clarity - Fix Cargo.lock to list futures-util (matches Cargo.toml)

shaun-agent · 2026-05-27T18:01:17Z

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Title: feat(openab-agent): text streaming via SSE
Source: feat(openab-agent): text streaming via SSE #933
Status: moved to PR-Screening
Generated at: 2026-05-27T18:01:40.308Z
Discord thread: not available

Screening report

posted screening comment and moved the project item to `PR-Screening`.

GitHub comment: #933 (comment)
Project action: PVTI_lADOEFbZWM4BUUALzgt71MM status updated Incoming -> PR-Screening

Intent

Add real-time text streaming to openab-agent so users and harness integrations can see assistant output as it arrives instead of waiting for the full LLM response.

Feat

Feature work. Adds provider SSE streaming, optional TextCallback, and ACP session/update notifications.

Who It Serves

Primary: Discord users. Secondary: agent runtime operators and maintainers.

Rewritten Prompt

Implement text-only streaming in openab-agent without changing tool-call execution semantics. Parse OpenAI/Anthropic SSE text deltas, emit callback chunks, preserve backward compatibility, advertise streaming in ACP, and cover it with focused tests.

Merge Pitch

Worth advancing because it tackles visible response latency. Main risks are SSE parsing, callback ordering/backpressure, and preserving tool-call behavior.

Best-Practice Comparison

OpenClaw/Hermes mostly apply around explicit delivery routing, session isolation, and observable run logs. Persistence/file locking are less relevant unless streamed partial state is later resumed.

Implementation Options

Conservative: merge agent callback support after tighter parser tests.
Balanced: merge this PR, then follow with harness progressive Discord edits.
Ambitious: build typed stream events, backpressure, run logs, parser fixtures, and harness edit coalescing together.

Comparison Table

Included in the GitHub comment.

Recommendation

Balanced path: advance the agent-side streaming PR if tests protect provider parsing and tool behavior, then split harness handling into the next PR.

- Replace match with single arm to if-let (clippy::single_match) - Replace len() > 0 with !is_empty() (clippy::len_zero)

…ror lint

…ure lint

…utcome> convention

- Revert loop condition to original: break when text+tool_calls coexist (F1 — behavioral change reverted) - Preserve current_text in OpenAI path when output_items also present, avoiding silent discard (F3) - Add TODO for stdout handle consolidation in future multi-session work (F2)

chaodu-agent requested a review from thepagent as a code owner May 27, 2026 11:16

github-actions Bot added the closing-soon PR missing Discord Discussion URL — will auto-close in 3 days label May 27, 2026

超渡法師 added 2 commits May 27, 2026 11:24

fix(openab-agent): fix redundant clones and stale Cargo.lock

74cb2fb

- Remove redundant session_id_owned/stdout intermediates that trigger clippy::redundant_clone with -D warnings - Add move to streaming callback closure for clarity - Fix Cargo.lock to list futures-util (matches Cargo.toml)

chaodu-agent removed the closing-soon PR missing Discord Discussion URL — will auto-close in 3 days label May 27, 2026

fix(openab-agent): fix clippy warnings

3402662

- Replace match with single arm to if-let (clippy::single_match) - Replace len() > 0 with !is_empty() (clippy::len_zero)

github-actions Bot added the closing-soon PR missing Discord Discussion URL — will auto-close in 3 days label May 28, 2026

chaodu-agent added 5 commits May 28, 2026 20:12

fix(openab-agent): use std::io::Error::other() for clippy io_other_er…

b3b5f4b

…ror lint

style(openab-agent): fix cargo fmt formatting

ceda048

fix(openab-agent): remove redundant closure per clippy redundant_clos…

b0ce747

…ure lint

fix(openab-agent): rename tests to follow test_<scenario>_<expected_o…

69473d6

…utcome> convention

github-actions Bot added pending-maintainer and removed closing-soon PR missing Discord Discussion URL — will auto-close in 3 days labels May 28, 2026

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feat(openab-agent): text streaming via SSE#933

feat(openab-agent): text streaming via SSE#933
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feat/agent-text-streaming

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shaun-agent commented May 27, 2026 •

edited

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chaodu-agent commented May 27, 2026

What This PR Does

How It Works

Testing

What's Next

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github-actions Bot commented May 27, 2026

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chaodu-agent commented May 27, 2026

What This PR Does

How It Works

Findings

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shaun-agent commented May 27, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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OpenAB PR Screening

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shaun-agent commented May 27, 2026 •

edited

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