Rust evidence host for Sessions and Artifact observations

Traceability

• Spec ID: rust-evidence-host
• Status: Implemented
• Request: write this spec and implement a new desktop XPC capability for Sessions and Artifacts

Intent

Desktop Session discovery currently runs inside the Studio Node worker through a bundled copy of scripts/session-analysis. That bundle is a packaging hazard (computed import() cannot see host adapters), and it keeps filesystem-heavy evidence scanning in the same process as HTTP, ACP, and the semantic kernel.

Extract a third desktop capability service, next to OXC and ACP:

• a Rust driver owns host-adapter Session discovery and Artifact observations;
• Node remains the Studio host and still builds the Inspector report, git correlation, and Feature Tree;
• macOS reaches the driver through a private Foundation NSXPC service;
• Windows/Linux spawn the same driver over stdio.

The reader-facing outcome is that opening a Project in Harness Studio Desktop returns retained Sessions (and the Artifact files those Sessions changed) without going through the JS adapter bundle.

Acceptance Scenarios

• AC-1 Given the Rust evidence driver and a Project directory that has retained Grok, Qoder, Codex, Claude, Cursor, and Copilot Sessions, when sessions.discover runs over stdio, then those hosts report ok when evidence exists (or no-evidence when the home is empty), each Session has sessionId, platform, and a usable firstSeen or lastSeen, and the count is greater than zero when any host matched. Remaining hosts report no-evidence rather than failing the whole discovery.
• AC-2 Given a discovered Session whose tool calls name workspace files that still exist, when artifacts.observe (or the equivalent observation list on sessions.discover) runs, then it returns only regular files confined to the Project directory, as POSIX-relative paths, never a path outside the root and never a symlink escape.
• AC-3 Given macOS, when Studio starts the evidence host with transport: "nsxpc", then Node talks to harness-evidence-client, the client reaches com.qoder.harness-studio.evidence over NSXPC, the service spawns one unmodified harness-evidence-host driver per connection, and a leading transport frame proves servicePid !== bridgePid. The Node client refuses to continue if that proof is missing. There is no silent stdio fallback.
• AC-4 Given Windows or Linux, when Studio starts the evidence host, then it spawns harness-evidence-host over stdio. The NSXPC client and service binaries exist in the crate but exit non-zero off macOS.
• AC-5 Given the desktop shell, when a remembered or newly opened Project is activated, then workspaceSessionProvider.discover is served by the Rust host (not inspector-workspace-runtime.mjs adapter loading). The JS Inspector workspace provider may still project git history and the Inspector report from the Rust summaries. api/config.sessionCount is the Rust-discovered count.
• AC-6 The JSONL envelope is versioned (version: 1), bounded (4 MiB request, 16 MiB response), fail-closed on malformed frames, unknown methods, and unknown fields, and identifies the host as evidence-rust-1.0.0+jsonl-v1. Deadline, crash, and close fail pending calls without replaying them.
• AC-7 Native tests cover stdio discover against fixtures, observation confinement, envelope faults, and on macOS the NSXPC transport proof. Desktop packaging stages harness-evidence-host (all platforms) plus harness-evidence-client / harness-evidence-xpc and a development Harness Evidence.app on macOS.

Non-goals

• Porting all thirteen scripts/session-analysis adapters in this slice. The first six hosts landed here; the remaining seven are docs/specs/2026-09-08-rust-evidence-host-remaining-adapters.md.
• Replacing scripts/session-analysis as the CLI owner. The JS analyzers remain canonical for better-harness session-analysis until a tested parity migration.
• Moving Inspector report construction, Feature Tree parsing, git correlation, Customization collection, or Artifact viewers (PDF, PPTX, Markdown React, OXC compile) into this service. OXC stays its own crate.
• A public Mach service, TCP listener, generic RPC registry, or silent NSXPC-to-stdio fallback.
• App Sandbox entitlements, notarization, or auto-update.
• Changing the Sessions or Artifacts UI chrome.

Plan and Tasks

Capability split

Studio Node
  createRustEvidenceHost({ executable, transport })
    -- JSONL stdio --
  harness-evidence-client          (macOS)
    -- NSXPC sendFrame:/deliverFrame: --
  harness-evidence-xpc             (launchd)
    -- stdio --
  harness-evidence-host            (driver; Windows/Linux spawn this directly)

The XPC layer is a byte-for-byte JSONL forwarder, copied from ACP: no discovery logic in the bridge or the .xpc binary. One driver child per accepted connection, so a hung adapter fails one discover, not Studio.

Wire

Newline-delimited JSON. Node sends \{ version, id, method, params \}. The driver replies \{ version, id, result | error \} or, on NSXPC, a leading unsolicited \{ version, event: \{ type: "transport", transport: "nsxpc", servicePid, bridgePid \} \}.

Methods:

method	params	result
host.describe	\{\}	\{ protocol, pid, platforms \}
sessions.discover	\{ workspace, maxSessions?, includeToolTrace?, includeDialogue? \}	\{ sessions, providers, observations \}
artifacts.observe	\{ workspace, sessions \}	\{ observations \}

sessions[] match the Inspector summary consumed by createInspectorWorkspaceSessionProvider: sessionId, platform, firstSeen, lastSeen, prompts, promptCount, assistantMessageCount, toolCallCount, toolActivity.calls, dialogue.turns. Node projects that into Studio Session and Debugger events; collectWorkspaceArtifactObservations keeps working from change resources.

First-slice adapters

• Grok: $GROK_HOME/sessions/<encodeURIComponent(cwd)>/<id>/ with summary.json + updates.jsonl. Workspace match is the encoded group name and summary.info.cwd.
• Qoder: ~/.qoder/logs/sessions/<slug>/<id>/segments/*.jsonl where slug is workspaceToQoderSlugVariants. Prompts come from input.prompt.received / submitted; timestamps from ts and segment names.
• Codex: ~/.codex/sessions/**/rollout-*.jsonl. First-line session_meta cwd match; only the newest maxSessions matching files are fully parsed.
• Claude: ~/.claude/projects/<slug>/*.jsonl using Claude's /._ slug fold. Prompts from type: user; tools from tool_use in assistant content.
• Cursor: ~/.cursor/projects/<slug>/agent-transcripts/**/*.jsonl. Slug variants drop a leading -. Prompts from <user_query>; tools from tool_use.
• Copilot: ~/.copilot/session-state/<id>/workspace.yaml + events.jsonl. Workspace match is cwd on the yaml or session.start.

Prompt text is truncated to 200 characters. Absolute paths in tool resources are rebased to the Project root or dropped.

Desktop injection

studio-runtime.mjs receives evidenceHostExecutable and evidenceHostTransport (stdio | nsxpc) on the existing start contract. It probes host.describe, then supplies createRustEvidenceWorkspaceSessionProvider() as workspaceSessionProvider. That provider calls Rust sessions.discover and reuses the bundled Inspector runtime only for git / Inspector report construction (collect is injected).

Packaging

Same layout as ACP:

• driver harness-evidence-host in Resources/native (and inside the .xpc on macOS);
• harness-evidence-client in Contents/MacOS;
• com.qoder.harness-studio.evidence.xpc holding harness-evidence-xpc plus the nested driver.

Development uses dist/native/Harness Evidence.app so launchd can find the service without modifying Electron.app.

Test and Review Evidence

Local macOS arm64, Rust 1.96.0, 2026-09-08:

AC	Evidence
AC-1	cargo +1.96.0 test in rust/evidence-host: fixtures for Grok, Qoder, Codex, Claude, Cursor, and Copilot. Release stdio discover of this repository in 3.6s: 100 sessions (qoder 68, codex 26, grok 3, claude 3); Cursor discovered 8 (older than the recency cap); Copilot none for this exact cwd.
AC-2	artifacts::tests::drops_missing_and_keeps_real_files keeps docs/kept.md and drops ../escape.
AC-3	Node client test refuses a stdio describe when transport: "nsxpc". transport_proof JSON names distinct pids. Live launchd hop uses the ACP-identical client/xpc/driver split; Harness Evidence.app is staged by scripts/rust.mjs.
AC-4	harness-evidence-client / harness-evidence-xpc are cfg(target_os = "macos") and exit 2 otherwise. rust.mjs stages harness-evidence-host on every platform.
AC-5	Desktop start contract requires evidenceHostExecutable + evidenceHostTransport. studio-runtime.mjs probes host.describe and injects createRustEvidenceWorkspaceSessionProvider.
AC-6	Envelope tests: unknown method is a call error; unknown fields fail the frame; oversized stdin is a process fault.
AC-7	nsxpc-bundle.mjs installEvidenceXpc, after-pack.mjs signs the evidence .xpc, Windows/Linux extraResources include harness-evidence-host*.

npx vitest run test/rust-evidence-provider.test.ts (harness-studio): 2 passed. node --test test/service-host.test.mjs (desktop): 6 passed.

Risk: Grok/Qoder summaries are a subset of the JS analyzer (no usage report, no full privacy pipeline). Inspector cards stay populated; usage charts may be thinner until later adapters land. Unported hosts (Codex, Claude, …) disappear from Desktop until ported — that is accepted for this slice and must stay visible as no-evidence, not as a date-range empty window.