FEATURE_PARITY.md

Feature Parity: pi_agent_rust vs Pi Agent (TypeScript)

Purpose: Authoritative single-source-of-truth for implementation status. Last Updated: 2026-02-18 (implementation snapshot refresh) Release Claim Guardrail: This document is progress evidence only. Strict drop-in replacement language is blocked unless docs/evidence/dropin-certification-verdict.json reports overall_verdict = CERTIFIED.

Status Legend

Status	Meaning
✅ Implemented	Feature exists, covered by tests
🔶 Partial	Some functionality present, known gaps remain
❌ Missing	In scope but not yet implemented
⬜ Out of Scope	Intentionally excluded from this port

---

Executive Summary

Category	Implemented	Partial	Missing	Out of Scope	Total
Core Types	8	0	0	0	8
Provider Layer	18	0	0	9	27
Tools (7 total)	7	0	0	0	7
Agent Runtime	7	0	0	0	7
Session Management	10	0	0	0	10
CLI	10	0	0	0	10
Resources & Customization	8	0	0	0	8
Extensions Runtime	12	0	0	0	12
TUI	18	0	0	2	20
Configuration	9	0	0	0	9
Authentication	8	0	0	0	8

---

1. Core Types (Message/Content/Usage)

Feature	Status	Rust Location	Tests	Notes
Message union (User/Assistant/ToolResult)	✅	src/model.rs:13-19	Unit	Complete enum with serde
UserMessage	✅	src/model.rs:22-27	Unit	Text or Blocks content
AssistantMessage	✅	src/model.rs:38-50	Unit	Full metadata
ToolResultMessage	✅	src/model.rs:53-63	Unit	Error flag, details
ContentBlock enum	✅	src/model.rs:86-93	Unit	Text/Thinking/Image/ToolCall
StopReason enum	✅	src/model.rs:70-79	Unit	All 5 variants
Usage tracking	✅	src/model.rs:145-166	Unit	Input/output/cache/cost
StreamEvent enum	✅	src/model.rs:172-232	Unit	All 12 event types

---

2. Provider Layer

2.1 Provider Trait

Feature	Status	Rust Location	Tests	Notes
Provider trait definition	✅	src/provider.rs:18-31	-	async_trait based
Context struct	✅	src/provider.rs:38-43	-	System prompt + messages + tools
StreamOptions	✅	src/provider.rs:62-72	-	Temperature, max_tokens, thinking
ToolDef struct	✅	src/provider.rs:49-55	-	JSON Schema parameters
Model definition	✅	src/provider.rs:108-121	-	Cost, context window, etc.
ThinkingLevel enum	✅	src/model.rs:239-265	Unit	6 levels with budgets
CacheRetention enum	✅	src/provider.rs:75-81	-	None/Short/Long

2.2 Provider Implementations

Provider	Status	Rust Location	Tests	Notes
Anthropic	✅	src/providers/anthropic.rs	Unit	Full streaming + thinking + tools
OpenAI	✅	src/providers/openai.rs	Unit	Full streaming + tool use
Google Gemini	✅	src/providers/gemini.rs	4	Full streaming + tool use
Azure OpenAI	✅	src/providers/azure.rs	4	Full streaming + tool use
Amazon Bedrock	⬜	-	-	Low priority
Google Vertex	⬜	-	-	Low priority
GitHub Copilot	⬜	-	-	OAuth complexity
XAI	⬜	-	-	Low priority
Groq	⬜	-	-	Low priority
Cerebras	⬜	-	-	Low priority
OpenRouter	⬜	-	-	Low priority
Mistral	⬜	-	-	Low priority
Custom providers	⬜	-	-	Defer

2.3 Streaming Implementation

Feature	Status	Location	Notes
SSE parsing (Anthropic)	✅	anthropic.rs	asupersync HTTP stream (src/http/client.rs) + src/sse.rs
SSE parser module	✅	src/sse.rs	Custom parser for asupersync migration
Text delta streaming	✅	anthropic.rs:339-352	Real-time text
Thinking delta streaming	✅	anthropic.rs:354-367	Extended thinking
Tool call streaming	✅	anthropic.rs:368-382	JSON accumulation
Usage updates	✅	anthropic.rs:430-448	Token counts
Error event handling	✅	anthropic.rs:258-266	API errors

---

3. Built-in Tools

Tool	Status	Rust Location	Tests	Conformance Tests
read	✅	src/tools.rs	4	✅ test_read_*
bash	✅	src/tools.rs	3	✅ test_bash_*
edit	✅	src/tools.rs	3	✅ test_edit_*
write	✅	src/tools.rs	2	✅ test_write_*
grep	✅	src/tools.rs	3	✅ test_grep_*
find	✅	src/tools.rs	2	✅ test_find_*
ls	✅	src/tools.rs	3	✅ test_ls_*

3.1 Tool Feature Details

Feature	read	bash	edit	write	grep	find	ls
Basic operation	✅	✅	✅	✅	✅	✅	✅
Truncation (head/tail)	✅	✅	-	-	✅	✅	✅
Image support	✅	-	-	-	-	-	-
Streaming updates	-	✅	-	-	-	-	-
Line numbers	✅	-	-	-	✅	-	-
Fuzzy matching	-	-	✅	-	-	-	-
Path resolution	✅	✅	✅	✅	✅	✅	✅
~ expansion	✅	-	✅	✅	✅	✅	✅
macOS screenshot paths	✅	-	-	-	-	-	-

3.2 Truncation Constants

Constant	Value	Used By
DEFAULT_MAX_LINES	2000	read, bash, grep
DEFAULT_MAX_BYTES	50KB	read, bash, grep, find, ls
GREP_MAX_LINE_LENGTH	500	grep

---

4. Agent Runtime

Feature	Status	Rust Location	Tests	Notes
Agent struct	✅	src/agent.rs	Unit	Provider + tools + config
Agent loop	✅	src/agent.rs	-	Tool iteration limit
Tool execution	✅	src/agent.rs	Unit	Error handling
Event callbacks	✅	src/agent.rs	-	9 event types
Stream processing	✅	src/agent.rs	-	Delta handling
Context building	✅	src/agent.rs	-	System + history + tools
Abort handling	✅	src/agent.rs, src/main.rs, src/interactive.rs	-	Ctrl+C cancels in-flight requests

---

5. Session Management

Feature	Status	Rust Location	Tests	Notes
Session struct	✅	src/session.rs	-	Header + entries + path
SessionHeader	✅	src/session.rs	-	Version 3
JSONL persistence	✅	src/session.rs	-	Save/load
Entry types (7)	✅	src/session.rs	-	Message, ModelChange, etc.
Tree structure	✅	src/session.rs	7	Full parent/child navigation
CWD encoding	✅	src/session.rs	1	Session directory naming
Entry ID generation	✅	src/session.rs	-	8-char hex
Continue previous	✅	src/session.rs	-	Most recent by mtime
Session picker UI	✅	src/session_picker.rs	3	TUI picker with bubbletea
Branching/navigation	✅	src/session.rs	7	navigate_to, create_branch_from, list_leaves, branch_summary

---

6. CLI

Feature	Status	Rust Location	Tests	Notes
Argument parsing	✅	src/cli.rs	-	Clap derive
Subcommands	✅	src/cli.rs, src/main.rs	-	Install, Remove, Update, List, Config
@file arguments	✅	src/cli.rs	-	File inclusion
Message arguments	✅	src/cli.rs	-	Positional text
Tool selection	✅	src/cli.rs	-	--tools flag
Model listing	✅	src/main.rs	-	Table output
Session export	✅	src/main.rs	-	HTML export
Print mode	✅	src/main.rs	-	Single-shot mode
RPC mode	✅	src/main.rs, src/rpc.rs	tests/rpc_mode.rs	Headless stdin/stdout JSON protocol (prompt/steer/follow_up/state/stats/model/thinking/compact/bash/fork)
Package management	✅	src/package_manager.rs, src/main.rs	Unit	install/remove/update/list + settings updates + startup auto-install + resource resolution

---

6A. Resources & Customization

Feature	Status	Rust Location	Tests	Notes
Skills loader + validation	✅	src/resources.rs	Unit	Agent Skills frontmatter + diagnostics
Skills prompt inclusion	✅	src/main.rs	Unit	Appends <available_skills> if read tool enabled
Skill command expansion (/skill:name)	✅	src/resources.rs, src/interactive.rs	Unit	Expands to <skill ...> block
Prompt template loader	✅	src/resources.rs	Unit	Global/project + explicit paths
Prompt template expansion (/name args)	✅	src/resources.rs, src/interactive.rs	Unit	$1, $@, $ARGUMENTS, ${@:N}
Package resource discovery	✅	src/resources.rs	Unit	Reads package.json pi field or defaults
Themes discovery	✅	src/theme.rs, src/interactive.rs	Unit + tests/tui_state.rs	Loader + /theme switching
Themes hot reload	✅	src/interactive.rs	tests/tui_state.rs	/reload re-resolves and reapplies current theme

6B. Extensions Runtime

Feature	Status	Rust Location	Tests	Notes
Extension discovery (paths + packages)	✅	src/package_manager.rs, src/resources.rs	Unit	Resolves extensions/ sources from settings/auto-discovery/packages/CLI
Extension protocol (v1) + JSON schema	✅	src/extensions.rs, docs/schema/extension_protocol.json	Unit + tests/extensions_manifest.rs	ExtensionMessage::parse_and_validate + schema compilation tests
Compatibility scanner (Node API audit)	✅	src/extensions.rs, src/package_manager.rs	tests/ext_conformance_artifacts.rs	Emits compat ledgers when PI_EXT_COMPAT_SCAN is enabled
Capability manifest + policy	✅	src/extensions.rs	Unit + tests/extensions_manifest.rs	strict/prompt/permissive + scoped manifests (pi.ext.cap.v1)
FS connector (scoped, anti-escape)	✅	src/extensions.rs	Unit	Path traversal + symlink escape hardening
HTTP connector (policy-gated)	✅	src/connectors/http.rs	Unit	TLS/allowlist/denylist/size/timeouts
PiJS runtime (QuickJS)	✅	src/extensions_js.rs	Unit + tests/event_loop_conformance.rs	Deterministic scheduler + Promise bridge + budgets/timeouts
Promise hostcall bridge (pi.* → queue → completion)	✅	src/extensions_js.rs	Unit	pi.tool/exec/http/session/ui/events + setTimeout/clearTimeout
Hostcall ABI (host_call/host_result protocol)	✅	src/extensions.rs	Unit	Protocol types + validation exist; end-to-end dispatch wired
Extension UI bridge (select/confirm/input/editor)	✅	src/extensions.rs, src/interactive.rs, src/rpc.rs	Unit	UI request/response plumbing exists; runtime dispatch wired
Extension session API (get_state/messages/set_name)	✅	src/extensions.rs, src/interactive.rs	-	Trait + interactive impl exist; runtime dispatch wired
JS extension execution + registration (tools/commands/hooks)	✅	src/extensions_js.rs, src/extension_dispatcher.rs, src/agent.rs, src/interactive.rs	Unit + E2E	QuickJS runtime loads JS/TS extensions and supports tool/command registration + execution + event hooks

---

7. Configuration

Feature	Status	Rust Location	Tests	Notes
Config loading	✅	src/config.rs	-	Global + project merge
Settings struct	✅	src/config.rs	-	All fields optional
Default accessors	✅	src/config.rs	-	Fallback values
Compaction settings	✅	src/config.rs	-	enabled, reserve, keep
Retry settings	✅	src/config.rs	-	enabled, max, delays
Image settings	✅	src/config.rs	-	auto_resize, block
Terminal settings	✅	src/config.rs	-	show_images, clear
Thinking budgets	✅	src/config.rs	-	Per-level overrides
Environment variables	✅	src/config.rs	-	PI_CONFIG_PATH/PI_CODING_AGENT_DIR/PI_PACKAGE_DIR/PI_SESSIONS_DIR + provider API keys

---

8. Terminal UI

8.1 Non-Interactive Output (rich_rust)

Feature	Status	Rust Location	Tests	Notes
PiConsole wrapper	✅	src/tui.rs	3	rich_rust integration
Styled output (markup)	✅	src/tui.rs	-	Colors, bold, dim
Agent event rendering	✅	src/tui.rs	-	Text, thinking, tools, errors
Table rendering	✅	src/tui.rs	-	Via rich_rust Tables
Panel rendering	✅	src/tui.rs	-	Via rich_rust Panels
Rule rendering	✅	src/tui.rs	-	Horizontal dividers
Spinner styles	✅	src/tui.rs	1	Dots, line, simple

8.2 Interactive TUI (charmed_rust/bubbletea)

Feature	Status	Rust Location	Tests	Notes
PiApp Model	✅	src/interactive.rs	296+	Elm Architecture (296 tui_state + 226 lib unit tests)
TextInput with history	✅	src/interactive.rs	-	bubbles TextInput
Markdown rendering	✅	src/interactive.rs	-	glamour Dark style
Token/cost footer	✅	src/interactive.rs	-	Usage tracking
Spinner animation	✅	src/interactive.rs	-	bubbles spinner
Tool status display	✅	src/interactive.rs	-	Running tool indicator
Keyboard navigation	✅	src/interactive.rs	-	Up/Down history, Esc quit
Agent integration	✅	src/interactive.rs	-	Agent events wired; CLI interactive uses PiApp
Multi-line editor	✅	src/interactive.rs	-	TextArea with line wrapping
Slash command system	✅	src/interactive.rs	-	/help, /login, /logout, /clear, /model, /thinking, /exit, /history, /export, /session, /resume, /new, /copy, /name, /hotkeys
Viewport scrolling	✅	src/interactive.rs	-	Viewport with scroll_to_bottom()
Image display	⬜	-	-	Terminal dependent
Autocomplete	✅	src/autocomplete.rs, src/interactive.rs	tests/tui_state.rs	Tab-triggered dropdown + path completion

8.3 Interactive Commands (Slash)

Command	Status	Rust Location	Notes
/help	✅	src/interactive.rs	Help text
/clear	✅	src/interactive.rs	Clears in-memory conversation view
/model	✅	src/interactive.rs	Switch model/provider
/thinking	✅	src/interactive.rs	Set thinking level
/history	✅	src/interactive.rs	Show input history
/export	✅	src/interactive.rs	Export session to HTML
/exit / /quit	✅	src/interactive.rs	Exit Pi
/login	✅	src/interactive/commands.rs, src/auth.rs	Anthropic OAuth + OpenAI/Google API key + extension OAuth
/logout	✅	src/interactive.rs, src/auth.rs	Remove stored credentials
/session	✅	src/interactive.rs	Show session info (path/tokens/cost)
/resume	✅	src/interactive.rs	Session picker overlay (deletion disabled)
/new	✅	src/interactive.rs	Start new in-memory session
/name <name>	✅	src/interactive.rs	Set session display name
/copy	✅	src/interactive.rs	Clipboard support is feature-gated (--features clipboard)
/hotkeys	✅	src/interactive.rs	Show keybindings
/scoped-models	✅	src/interactive/commands.rs	Pattern matching + persistence to project settings
/settings	✅	src/interactive.rs	Shows effective settings + resource counts
/tree	✅	src/interactive.rs	List leaves and switch branch by id/index
/fork	✅	src/interactive.rs	Forks new session file from user message
/compact [prompt]	✅	src/interactive.rs, src/compaction.rs	Manual compaction
/share	✅	src/interactive/share.rs	HTML export + GitHub Gist upload via gh CLI
/reload	✅	src/interactive.rs, src/resources.rs	Reloads skills/prompts/themes + refreshes autocomplete
/changelog	✅	src/interactive.rs	Display changelog entries

---

9. Authentication

Feature	Status	Rust Location	Tests	Notes
API key from env	✅	src/auth.rs	-	ANTHROPIC_API_KEY, etc.
API key from flag	✅	src/main.rs	-	--api-key
auth.json storage	✅	src/auth.rs	-	File with 0600 perms
File locking	✅	src/auth.rs	-	Exclusive lock with timeout
Key resolution	✅	src/auth.rs	-	override > auth.json > env
Multi-provider keys	✅	src/auth.rs	-	12 auth provider families supported
OAuth flow	✅	src/auth.rs, src/interactive/commands.rs	Unit	Anthropic PKCE + extension-registered providers
Token refresh	✅	src/auth.rs, src/main.rs	Unit	Auto-refresh on startup for all OAuth providers

---

10. Error Handling

Feature	Status	Rust Location	Tests	Notes
Error enum	✅	src/error.rs	-	thiserror based
Config errors	✅	src/error.rs	-
Session errors	✅	src/error.rs	-	Including NotFound
Provider errors	✅	src/error.rs	-	Provider + message
Auth errors	✅	src/error.rs	-
Tool errors	✅	src/error.rs	-	Tool name + message
Validation errors	✅	src/error.rs	-
IO/JSON/HTTP errors	✅	src/error.rs	-	From impls

---

Test Coverage Summary

Category	Unit Tests	Integration Tests	Fixture Cases	Total
Core types	4	0	0	4
Provider (Anthropic)	2	0	0	2
Provider (OpenAI)	3	0	0	3
Provider (Gemini)	4	0	0	4
Provider (Azure)	4	0	0	4
SSE parser	11	0	0	11
Tools	5	20	122	147
CLI flags (fixtures)	0	0	17	17
TUI (rich_rust)	3	0	0	3
TUI (interactive lib)	226	0	0	226
TUI (tui_state integration)	0	296	0	296
TUI (e2e_tui_perf)	0	103	0	103
TUI (session picker)	3	0	0	3
TUI (perf unit: FrameTiming/Cache/Buffers)	47	0	0	47
Session (branching)	7	0	0	7
Agent	2	0	0	2
Conformance infra	6	0	0	6
Extensions	2	0	0	2
Other lib tests	2,800+	0	0	2,800+
Total (lib)	3,319	-	-	3,319
Total (all targets)	3,319+	399+	139	3,857+

All tests pass (cargo test --lib: 3,319 pass; tui_state: 296 pass; e2e_tui_perf: 103 pass)

---

Conformance Testing Status

Component	Has Fixture Tests	Fixture File	Cases	Status
read tool	✅ Yes	read_tool.json	23	✅ All pass
write tool	✅ Yes	write_tool.json	7	✅ All pass
edit tool	✅ Yes	edit_tool.json	23	✅ All pass
bash tool	✅ Yes	bash_tool.json	34	✅ All pass
grep tool	✅ Yes	grep_tool.json	12	✅ All pass
find tool	✅ Yes	find_tool.json	6	✅ All pass
ls tool	✅ Yes	ls_tool.json	8	✅ All pass
truncation	✅ Yes	truncation.json	9	✅ All pass
Session format	✅ Yes	tests/session_conformance.rs	28	✅ All pass
Provider responses	✅ Yes	tests/provider_streaming.rs	4	✅ All pass (VCR)
CLI flags	✅ Yes	cli_flags.json	17	✅ All pass
Total	11/11	-	171	✅

Fixture Schema

Fixtures are JSON files in tests/conformance/fixtures/ with this structure:

{
  "version": "1.0",
  "tool": "tool_name",
  "cases": [
    {
      "name": "test_name",
      "setup": [{"type": "create_file", "path": "...", "content": "..."}],
      "input": {"param": "value"},
      "expected": {
        "content_contains": ["..."],
        "content_regex": "...",
        "details_exact": {"key": "value"}
      }
    }
  ]
}

---

Performance Targets

Metric	Target	Current	Status
Startup time	<100ms	13ms (pi --version)	✅
Binary size (release)	<20MB	8.3MB	✅
TUI framerate	60fps	Instrumented (PERF-3: frame timing telemetry)	✅
Frame budget	<16ms	Enforced (PERF-4: auto-degrades when exceeded)	✅
Memory (idle)	<50MB	Monitored (PERF-6: RSS-based pressure detection)	✅

Performance Features (PERF Track — Complete)

Feature	Bead	Description	Status
Message render cache	PERF-1	Per-message memoization with generation-based invalidation	✅
Incremental prefix	PERF-2	Streaming fast path: cached prefix + append-only tail	✅
Frame timing telemetry	PERF-3	Microsecond-precision instrumentation of view()/update()	✅
Frame budget + degradation	PERF-4	Auto-degrade rendering when frames exceed 16ms budget	✅
Memory pressure detection	PERF-6	RSS monitoring, progressive collapse at thresholds	✅
Buffer pre-allocation	PERF-7	Reusable render buffers, capacity hints, zero-copy paths	✅
Criterion benchmarks	PERF-8	Benchmark suite for all critical rendering paths	✅
CI regression gate	PERF-9	Fail CI on >20% performance regression	✅
Cross-platform fallbacks	PERF-CROSS	Graceful degradation when /proc unavailable (macOS/Windows)	✅

---

Next Steps (Priority Order)

1. Complete print mode - Non-interactive single response ✅ Done
2. Add OpenAI provider - Second provider implementation ✅ Done
3. Implement auth.json - Credential storage ✅ Done (src/auth.rs)
4. Session picker UI - Basic TUI for --resume ✅ Done (src/session_picker.rs)
5. Branching/navigation - Tree operations ✅ Done (src/session.rs)
6. Benchmark harness - Performance validation ✅ Done (benches/tools.rs, BENCHMARKS.md)
7. Conformance fixtures - TypeScript reference capture ✅ Done (tests/conformance/)