Add MCP server endpoint

Gemfile

@@ -7,6 +7,7 @@ gem 'puma'
 gem 'bootsnap', require: false
 gem "propshaft"
 gem 'aws-sdk-s3', '~> 1'
+gem 'mcp'
 
 group :development, :test do
   gem 'sqlite3'

Gemfile.lock

@@ -108,6 +108,7 @@ GEM
     erubi (1.13.1)
     globalid (1.3.0)
       activesupport (>= 6.1)
+    hana (1.3.7)
     i18n (1.14.8)
       concurrent-ruby (~> 1.0)
     io-console (0.8.2)
@@ -118,6 +119,11 @@ GEM
       reline (>= 0.4.2)
     jmespath (1.6.2)
     json (2.19.9)
+    json_schemer (2.5.0)
+      bigdecimal
+      hana (~> 1.3)
+      regexp_parser (~> 2.0)
+      simpleidn (~> 0.2)
     logger (1.7.0)
     loofah (2.25.2)
       crass (~> 1.0.2)
@@ -129,6 +135,8 @@ GEM
       net-pop
       net-smtp
     marcel (1.1.0)
+    mcp (1.0.0)
+      json_schemer (>= 2.4)
     mini_mime (1.1.5)
     mini_portile2 (2.8.9)
     minitest (6.0.5)
@@ -229,9 +237,11 @@ GEM
       erb
       psych (>= 4.0.0)
       tsort
+    regexp_parser (2.12.0)
     reline (0.6.3)
       io-console (~> 0.5)
     securerandom (0.4.1)
+    simpleidn (0.2.3)
     sqlite3 (2.9.5)
       mini_portile2 (~> 2.8.0)
     sqlite3 (2.9.5-aarch64-linux-gnu)
@@ -287,6 +297,7 @@ PLATFORMS
 DEPENDENCIES
   aws-sdk-s3 (~> 1)
   bootsnap
+  mcp
   pg
   propshaft
   puma

README.md

@@ -10,6 +10,18 @@ To run this on local machine, following command can run development server:
 % env DATABASE_URL=`heroku config:get -a rubyci DATABASE_URL` rails s
 ```
 
+# MCP endpoint
+
+`POST /mcp` serves the Model Context Protocol over Streamable HTTP (stateless, read-only, no authentication).
+
+```
+claude mcp add --transport http rubyci https://rubyci.org/mcp
+```
+
+Tools: `list_servers`, `current_status`, `report_history`, `search_failures`, `find_failure_origin`, `failing_servers`, `get_log_excerpt`.
+
+Typical triage flow: `current_status` shows what is failing now, `failing_servers` shows how widespread a specific failure is, and `find_failure_origin` returns the first bad build with a github.com/ruby/ruby compare URL for the suspect commit range. Combine with a GitHub MCP server to enumerate commits in that range and a bugs.ruby-lang.org MCP server to search or file issues.
+
 # Storage note
 
 * To optimize S3 Access, extra directories should have 'o' character like 'log' and 'lcov'.

app/controllers/mcp_controller.rb

@@ -0,0 +1,52 @@
+# MCP (Model Context Protocol) endpoint. Streamable HTTP transport in
+# stateless mode: each POST is self-contained, so it works across multiple
+# Puma processes without sticky sessions. Read-only, no authentication,
+# same public posture as /reports and /search.
+class McpController < ApplicationController
+  skip_forgery_protection
+
+  TOOLS = [
+    McpTools::ListServers,
+    McpTools::CurrentStatus,
+    McpTools::ReportHistory,
+    McpTools::SearchFailures,
+    McpTools::FindFailureOrigin,
+    McpTools::FailingServers,
+    McpTools::GetLogExcerpt,
+  ].freeze
+
+  INSTRUCTIONS = <<~TEXT.freeze
+    rubyci.org aggregates chkbuild CI results for ruby/ruby. Typical triage flow:
+    current_status to see what is failing now, failing_servers to see how widespread
+    a specific failure is, then find_failure_origin to get the first bad build and a
+    github.com/ruby/ruby compare URL for the suspect commit range. Chain the results
+    with a GitHub MCP server (enumerate commits in compare_url, inspect diffs) and a
+    bugs.ruby-lang.org MCP server (search or file issues using the matching_line
+    snippet and commit SHA).
+  TEXT
+
+  def handle
+    server = MCP::Server.new(
+      name: "rubyci",
+      version: "1.0.0",
+      instructions: INSTRUCTIONS,
+      tools: TOOLS,
+    )
+    transport = MCP::Server::Transports::StreamableHTTPTransport.new(
+      server,
+      stateless: true,
+      enable_json_response: true,
+      # This is a public server; host-header validation is meant for local
+      # stdio-adjacent deployments and would reject rubyci.org.
+      dns_rebinding_protection: false,
+    )
+    status, headers, body = transport.handle_request(request)
+    headers.each { |k, v| response.set_header(k, v) unless k.casecmp?("content-length") }
+    body = Array(body).join
+    if body.empty?
+      head status
+    else
+      render body: body, status: status
+    end
+  end
+end

app/controllers/reports_controller.rb

@@ -43,7 +43,7 @@ def current
     if stale?(:last_modified => last_modified, :etag => last_modified.to_s, :public => true)
       @reports = Report.includes(:server).order('reports.branch DESC, servers.ordinal ASC, reports.option ASC').
         references(:server).
-        where('reports.id IN (SELECT MAX(R.id) FROM reports R WHERE R.datetime > ? GROUP BY R.server_id, R.branch, R.option)', 14.days.ago).all
+        latest_per_config(14.days.ago).all
       @reports = @reports.to_a.delete_if{|report| report.server.nil? }
 
       @reports = filter_deprecated(@reports)

app/models/report.rb

@@ -7,6 +7,11 @@
 class Report < ApplicationRecord
   belongs_to :server
   has_one :log_excerpt, dependent: :delete
+  # Latest report for each (server, branch, option) configuration since the
+  # given time. Shared by ReportsController#current and the MCP endpoint.
+  scope :latest_per_config, ->(since) {
+    where('reports.id IN (SELECT MAX(R.id) FROM reports R WHERE R.datetime > ? GROUP BY R.server_id, R.branch, R.option)', since)
+  }
   validates :server_id, :presence => true
   # SVN revision number or full 40-hex git commit SHA
   validates :revision, :format => { :with => /\A(?:\d+|\h{40})\z/ }, allow_nil: true
@@ -102,6 +107,40 @@ def diffstat
     summary[/((?:no )?diff[^)>]*)/, 1]
   end
 
+  def success?
+    if (result = meta&.[]("result"))
+      result == "success"
+    else
+      # scan_recent_ltsv appends " success" to summary for successful builds
+      summary.include?(" success")
+    end
+  end
+
+  def git_sha
+    sha1 if sha1&.match?(/\A\h{40}\z/)
+  end
+
+  # Compact serialization for the MCP endpoint. Excludes the raw ltsv/summary
+  # blobs; hands back external URLs instead of log contents.
+  def as_mcp_json
+    {
+      id: id,
+      server: server&.name,
+      server_id: server_id,
+      branch: branch,
+      option: option,
+      datetime: datetime.utc.iso8601,
+      revision: revision,
+      commit_sha: git_sha,
+      result: success? ? "success" : "failure",
+      summary: shortsummary || summary,
+      failures: { build: build, test: test, testall: testall, rubyspec: rubyspec }.compact,
+      log_url: (loguri if server),
+      fail_html_url: (failuri if server),
+      commit_url: revisionuri,
+    }.compact
+  end
+
   def depsuffixed_name
     if /vc/ =~ server.uri
       # mswin

app/tools/mcp_tools/current_status.rb

@@ -0,0 +1,26 @@
+module McpTools
+  class CurrentStatus < MCP::Tool
+    extend Helpers
+
+    tool_name "current_status"
+    description "Latest build result for each (server, branch, option) configuration within " \
+                "the last 14 days. Start here to see which configurations are currently failing."
+    input_schema(
+      properties: {
+        branch: { type: "string", description: "Filter by branch, e.g. 'master' or '3.4'" },
+        failures_only: { type: "boolean", description: "Return only failing configurations" },
+      },
+      required: [],
+    )
+    annotations(Helpers::READ_ONLY)
+
+    def self.call(branch: nil, failures_only: false, server_context: nil)
+      reports = Report.includes(:server).latest_per_config(14.days.ago).to_a
+      reports.reject! { |r| r.server.nil? || r.branch == 'trunk' }
+      reports.select! { |r| r.branch == branch } if branch.present?
+      reports.reject!(&:success?) if failures_only
+      reports.sort_by! { |r| [r.branch, r.server.ordinal, r.option.to_s] }
+      json_response(count: reports.size, reports: reports.map(&:as_mcp_json))
+    end
+  end
+end

app/tools/mcp_tools/failing_servers.rb

@@ -0,0 +1,69 @@
+module McpTools
+  class FailingServers < MCP::Tool
+    extend Helpers
+
+    MAX_MATCHES = 2000
+
+    tool_name "failing_servers"
+    description "Given a failure log substring (e.g. a test name or assertion message), list the " \
+                "(server, branch, option) configurations where that failure occurred, with first " \
+                "and last occurrence and whether the latest build of each configuration still has " \
+                "it. Distinguishes an environment-specific failure from a global regression."
+    input_schema(
+      properties: {
+        query: { type: "string", description: "Substring to match in failure logs" },
+        branch: { type: "string", description: "Filter by branch, e.g. 'master'" },
+        from: { type: "string", description: "Start date (YYYY-MM-DD, UTC; default 14 days ago)" },
+        to: { type: "string", description: "End date (YYYY-MM-DD, UTC, inclusive)" },
+      },
+      required: ["query"],
+    )
+    annotations(Helpers::READ_ONLY)
+
+    def self.call(query:, branch: nil, from: nil, to: nil, server_context: nil)
+      return error_response("query must not be blank") if query.strip.empty?
+      from_t = parse_time(from) || 14.days.ago.utc
+      to_t = parse_time(to, end_of_day: true)
+
+      scope = Report.joins(:log_excerpt).merge(LogExcerpt.content_match(query)).
+        includes(:server).
+        where("reports.datetime >= ?", from_t).
+        order("reports.datetime ASC").limit(MAX_MATCHES)
+      scope = scope.where("reports.datetime <= ?", to_t) if to_t
+      scope = scope.where(branch: branch) if branch.present?
+      matches = scope.to_a.reject { |r| r.server.nil? }
+      if matches.empty?
+        return json_response(query: query, branch: branch, message: "No matching failure in the window")
+      end
+      match_ids = matches.map(&:id).to_set
+
+      configs = matches.group_by { |r| [r.server_id, r.branch, r.option] }.map do |(server_id, br, opt), reports|
+        first = reports.first
+        last = reports.last
+        latest = Report.where(server_id: server_id, branch: br, option: opt).order(datetime: :desc).first
+        {
+          server: first.server.name,
+          server_id: server_id,
+          branch: br,
+          option: opt,
+          occurrences: reports.size,
+          still_failing: match_ids.include?(latest.id),
+          first_seen: first.as_mcp_json,
+          last_seen: last.as_mcp_json.merge(matching_line: last.log_excerpt&.matching_line(query)).compact,
+        }
+      end
+      configs.sort_by! { |c| c[:first_seen][:datetime] }
+
+      json_response(
+        query: query,
+        branch: branch,
+        from: from_t.iso8601,
+        to: to_t&.iso8601,
+        config_count: configs.size,
+        total_occurrences: matches.size,
+        truncated: matches.size >= MAX_MATCHES,
+        configs: configs,
+      )
+    end
+  end
+end