---
phase: 14-preview-bridge-infrastructure
verified: 2026-02-24T23:00:00Z
status: passed
score: 15/15 must-haves verified
re_verification: false
---

# Phase 14: Preview Bridge Infrastructure Verification Report

**Phase Goal:** Developer can run `cargo pmcp preview`, see their widget rendered in an iframe, and click UI elements that fire real MCP tool calls through the bridge proxy
**Verified:** 2026-02-24
**Status:** PASSED
**Re-verification:** No — initial verification

---

## Goal Achievement

### Observable Truths

| # | Truth | Status | Evidence |
|---|-------|--------|----------|
| 1 | MCP session is initialized exactly once on first proxy call and reused for all subsequent calls | VERIFIED | `RwLock<Option<SessionInfo>>` at proxy.rs:139; double-checked locking in `ensure_initialized()` (lines 162-235) |
| 2 | Proxy can list resources from MCP server via resources/list JSON-RPC | VERIFIED | `list_resources()` sends `"resources/list"` at proxy.rs:385 |
| 3 | Proxy can read resource content from MCP server via resources/read JSON-RPC | VERIFIED | `read_resource()` sends `"resources/read"` at proxy.rs:404 |
| 4 | API endpoints /api/resources and /api/resources/read return resource data as JSON | VERIFIED | Routes registered at server.rs:78-79; handlers at api.rs:84-110 |
| 5 | API endpoint /api/reconnect resets session and re-initializes | VERIFIED | `reconnect()` handler calls `reset_session()` then `list_tools()` at api.rs:114-126; route at server.rs:81 |
| 6 | notifications/initialized is sent after successful session initialization | VERIFIED | Fire-and-forget call at proxy.rs:232: `let _ = self.send_notification("notifications/initialized").await;` |
| 7 | Developer runs cargo pmcp preview and immediately sees widget HTML rendered in the iframe from the first UI resource | VERIFIED | `initSession()` fetches `/api/resources` and calls `loadResourceWidget(uiResources[0].uri)` at index.html:928-930; `cargo-pmcp/src/commands/preview.rs` wires CLI to `PreviewServer::start()` |
| 8 | When server has multiple UI resources, a picker above the tool list lets the developer switch between them | VERIFIED | `renderResourcePicker()` renders clickable `.resource-entry` list when `uiResources.length > 1` at index.html:962-978 |
| 9 | When server has only one UI resource, just a label shows (no picker dropdown) | VERIFIED | Single-resource branch at index.html:955-960: shows `resource-label`, hides `resource-list` |
| 10 | Each bridge callTool invocation logs an expandable entry in the Network tab with tool name, args, response, and duration | VERIFIED | `logBridgeCall()` creates `<details>/<summary>` with tool name, duration, args `<pre>`, response `<pre>` at index.html:1550-1579; bridge wires it at index.html:1371 |
| 11 | Network tab shows a badge count when new bridge calls happen while another tab is active | VERIFIED | `updateNetworkBadge()` adds/updates `.badge` span at index.html:1581-1602; badge auto-clears on Network tab selection at index.html:1170-1173 |
| 12 | Connected/disconnected status dot in the header reflects actual MCP session state | VERIFIED | `setStatus()` applies `.connected`, `.disconnected`, `.reconnecting` classes at index.html:1073-1091; wired in `initSession()` success/error paths |
| 13 | Reconnect button in the header resets session and refreshes tools/resources | VERIFIED | `handleReconnect()` calls `POST /api/reconnect` then `initSession()` at index.html:1061-1071; button wired at index.html:1056-1058 |
| 14 | When MCP server is unreachable, inline error message with Retry button shows in widget area | VERIFIED | `showWidgetError()` creates `.widget-error` div with `.widget-error-retry` button at index.html:1010-1040; Retry calls `loadResourceWidget(activeResourceUri)` |
| 15 | Per-tab clear buttons exist for Console, Network, and Events tabs | VERIFIED | `data-clear="console"`, `data-clear="network"`, `data-clear="events"` buttons in HTML at index.html:811-823; handlers at index.html:1177-1194 |

**Score:** 15/15 truths verified

---

## Required Artifacts

### Plan 01 Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `crates/mcp-preview/src/proxy.rs` | McpProxy with session persistence, list_resources(), read_resource(), reset_session() | VERIFIED | All methods present and substantive; `RwLock<Option<SessionInfo>>` confirmed at line 139 |
| `crates/mcp-preview/src/handlers/api.rs` | list_resources, read_resource, reconnect handlers | VERIFIED | All 4 handlers present (list_resources, read_resource, reconnect, status); each delegates to proxy methods |
| `crates/mcp-preview/src/server.rs` | Routes for /api/resources, /api/resources/read, /api/reconnect | VERIFIED | All 4 routes registered at lines 78-82 |

### Plan 02 Artifacts

| Artifact | Expected | Status | Details |
|----------|----------|--------|---------|
| `crates/mcp-preview/assets/index.html` | Resource picker, auto-load, enhanced DevTools, connection status, reconnect | VERIFIED | All functions confirmed: `initSession`, `loadResourceWidget`, `renderResourcePicker`, `handleReconnect`, `showWidgetError`, `logBridgeCall`, `updateNetworkBadge` |

---

## Key Link Verification

### Plan 01 Key Links

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| `handlers/api.rs` | `proxy.rs` | `state.proxy.list_resources()` and `state.proxy.read_resource()` | WIRED | `state.proxy.list_resources().await` at api.rs:85; `state.proxy.read_resource()` at api.rs:106; `state.proxy.reset_session()` at api.rs:115 |
| `server.rs` | `handlers/api.rs` | Route registration for resource endpoints | WIRED | Routes `/api/resources`, `/api/resources/read`, `/api/reconnect`, `/api/status` registered at server.rs:78-82 |

### Plan 02 Key Links

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| `index.html` | `/api/resources` | `fetch` in `initSession()` | WIRED | `fetch('/api/resources')` at index.html:897 inside `initSession()` |
| `index.html` | `/api/resources/read` | `fetch` in `loadResourceWidget()` | WIRED | `fetch('/api/resources/read?uri=${...}')` at index.html:986 inside `loadResourceWidget()` |
| `index.html` | `/api/reconnect` | `fetch` in `handleReconnect()` | WIRED | `fetch('/api/reconnect', { method: 'POST' })` at index.html:1065 inside `handleReconnect()` |

### Additional Key Link: CLI to Preview Server

| From | To | Via | Status | Details |
|------|----|-----|--------|---------|
| `cargo-pmcp/src/commands/preview.rs` | `mcp_preview::PreviewServer::start()` | Direct call with config | WIRED | `mcp_preview::PreviewServer::start(config).await` at preview.rs:45; registered in `cargo-pmcp/src/commands/mod.rs` and dispatched in `main.rs:296` |

---

## Requirements Coverage

All 7 requirement IDs claimed across both plans are covered:

| Requirement | Source Plan | Description | Status | Evidence |
|-------------|-------------|-------------|--------|----------|
| PREV-01 | 14-02 | Developer can preview widget in iframe rendered from MCP resource URI via `cargo pmcp preview` | SATISFIED | `loadResourceWidget()` fetches resource, extracts HTML content, calls `loadWidget()` which sets `frame.srcdoc` |
| PREV-02 | 14-01 | Widget `window.mcpBridge.callTool()` calls route to real MCP server through preview proxy | SATISFIED | Bridge `callTool` in `wrapWidgetHtml()` fetches `/api/tools/call` which calls `state.proxy.call_tool()` which calls `ensure_initialized()` then sends JSON-RPC |
| PREV-03 | 14-01 | MCP proxy initializes session once and reuses across all subsequent requests | SATISFIED | `ensure_initialized()` with `RwLock<Option<SessionInfo>>` double-checked locking; all proxy methods call it |
| PREV-04 | 14-01 | Preview fetches widget HTML via `resources/read` proxy call to MCP server | SATISFIED | `read_resource()` sends `"resources/read"` JSON-RPC; `/api/resources/read` endpoint returns contents; frontend calls it in `loadResourceWidget()` |
| PREV-05 | 14-02 | DevTools panel updates in real time when bridge calls are made | SATISFIED | `logBridgeCall()` called in bridge `callTool()` after every call (success and error); creates expandable `<details>/<summary>` entry in Network tab |
| PREV-06 | 14-02 | Connection status indicator shows connected/disconnected state | SATISFIED | `setStatus()` applies CSS class to `#status-dot`; called on success (connected), error (disconnected), and reconnect (reconnecting) |
| PREV-07 | 14-02 | Resource picker shows multiple UI resources when server exposes more than one | SATISFIED | `renderResourcePicker()` branches on `uiResources.length`: 1 resource shows label only, multiple shows clickable list |

No orphaned requirements: REQUIREMENTS.md traceability table maps PREV-01 through PREV-07 exclusively to Phase 14, and all seven are covered by plans 14-01 and 14-02.

---

## Anti-Patterns Found

No anti-patterns detected across any modified files:

- Zero TODO/FIXME/HACK/PLACEHOLDER comments in `proxy.rs`, `handlers/api.rs`, `server.rs`, or `index.html`
- No empty implementations (`return null`, `return {}`, etc.)
- No stub handlers returning static data instead of real results
- No unconnected state variables

---

## Quality Gates

| Check | Status | Notes |
|-------|--------|-------|
| `cargo check -p mcp-preview` | PASSED | Compiled in 0.46s with no errors |
| `cargo clippy -p mcp-preview -- -D warnings` | PASSED | Zero warnings |
| `cargo fmt --check -p mcp-preview` | PASSED | No formatting violations |
| All 4 commit hashes verified | PASSED | d4e67a6, 17901f1, cc77347, dac1893 all in git history |

---

## Human Verification Required

The following items cannot be verified programmatically and require a running preview server with a real MCP server:

### 1. End-to-End Widget Render

**Test:** Run `cargo pmcp preview --url http://localhost:3000` against an MCP server that exposes an HTML resource (MIME type `text/html`). Open `http://localhost:8765` in a browser.
**Expected:** Widget HTML appears in the iframe immediately on page load without any manual interaction.
**Why human:** Requires live MCP server + browser; iframe `srcdoc` rendering cannot be asserted statically.

### 2. Bridge callTool Real Round-Trip

**Test:** In the rendered widget, trigger an interaction that calls `window.mcpBridge.callTool("some_tool", {...})`.
**Expected:** The Network tab in DevTools shows an expandable entry for the call with tool name, arguments, response JSON, and duration in ms.
**Why human:** Requires live iframe interaction and cross-frame communication to be observed.

### 3. Badge Count Behavior

**Test:** Switch to the Console tab, then trigger a bridge `callTool` from the widget.
**Expected:** A red badge number appears on the Network tab button. Clicking the Network tab removes the badge.
**Why human:** Requires live browser interaction to verify badge DOM update behavior.

### 4. Reconnect Flow

**Test:** Start preview, disconnect the MCP server, click the Reconnect button, restart the MCP server.
**Expected:** Status dot turns orange during reconnect attempt, then green on success; tools and resources reload.
**Why human:** Requires controlled network disruption to test the disconnected/reconnecting states.

---

## Gaps Summary

No gaps found. All 15 observable truths verified, all artifacts substantive and wired, all 7 requirements satisfied, no anti-patterns detected, quality gates pass.

---

_Verified: 2026-02-24_
_Verifier: Claude (gsd-verifier)_
