feat: make agent context paths configurable via env vars (#23878)

Replace hardcoded paths for instruction files, skills, and MCP config
with
values read from `CODER_AGENT_EXP_*` environment variables. Template
authors
configure paths via the existing `coder_agent` `env` block. The agent
resolves `~`, relative, and absolute paths locally, then serves the
resolved config over `GET /api/v0/context-config`. `chatd` fetches this
once per workspace attach and falls back to today's defaults for older
agents.

All path env vars are comma-separated, allowing multiple directories:

| Env Var | Default | Controls |
|---|---|---|
| `CODER_AGENT_EXP_INSTRUCTIONS_DIRS` | `~/.coder` | Dirs containing the
instruction file |
| `CODER_AGENT_EXP_INSTRUCTIONS_FILE` | `AGENTS.md` | Instruction file
name |
| `CODER_AGENT_EXP_SKILLS_DIRS` | `.agents/skills` | Skills directories
|
| `CODER_AGENT_EXP_SKILL_META_FILE` | `SKILL.md` | Skill metadata file
name |
| `CODER_AGENT_EXP_MCP_CONFIG_FILES` | `.mcp.json` | MCP config files |

### Example

```hcl
resource "coder_agent" "main" {
  os   = "linux"
  arch = "amd64"
  env = {
    CODER_AGENT_EXP_INSTRUCTIONS_DIRS  = "/opt/company/agent-config,~/.coder"
    CODER_AGENT_EXP_INSTRUCTIONS_FILE  = "CLAUDE.md"
    CODER_AGENT_EXP_SKILLS_DIRS        = "/opt/company/ai-skills,.agents/skills"
    CODER_AGENT_EXP_MCP_CONFIG_FILES   = "/opt/company/mcp.json,.mcp.json"
  }
}
```

<details>
<summary>Implementation Details</summary>

### Architecture

Follows the same pattern as MCP tool discovery:
agent resolves locally → exposes via HTTP → chatd consumes.

**Agent-side** (`agent/agentcontextconfig/`):
- `ResolvePath` / `ResolvePaths` handle `~`, relative, and absolute path
forms; returns `""` for relative paths when baseDir is empty
- `Config` reads env vars, falls back to defaults, resolves all paths
- `GET /api/v0/context-config` serves the resolved config as JSON

**chatd-side** (`coderd/x/chatd/`):
- Calls `conn.ContextConfig()` once on first workspace attach
- Falls back to hardcoded defaults on 404 (older agents)
- Iterates instruction dirs, skills dirs using resolved absolute paths
- `LSRelativityRoot` everywhere — no more home/root juggling

### Key design decisions

- **`EXP_` prefix**: env vars use `CODER_AGENT_EXP_*` to indicate
experimental status
- **Plural names**: comma-separated vars use plural names (`DIRS`,
`FILES`); single-value vars use singular (`FILE`)
- **Defaults in `workspacesdk`**: default constants live in
`codersdk/workspacesdk/` so both agent and server reference them without
cross-layer imports
- **`skillMetaFile` persistence**: stored on context-file parts via
`ContextFileSkillMetaFile` and restored on subsequent chat turns so
custom values survive across turns
- **Working dir dedup**: `slices.Contains` guard prevents reading the
same instruction file from both `InstructionsDirs` and the working
directory
- **MCP server dedup**: first-occurrence-wins dedup prevents leaking
duplicate connections from overlapping config files
- **ResolvePath safety**: returns `""` for relative paths when `baseDir`
is empty, so `ResolvePaths` filters them out

### Files changed

| File | Change |
|---|---|
| `agent/agentcontextconfig/` | New package — path resolution + HTTP
endpoint |
| `codersdk/workspacesdk/agentconn.go` | `ContextConfigResponse` type,
default constants, client method |
| `agent/agent.go` + `agent/api.go` | Wire up endpoint, pass config to
MCP |
| `agent/x/agentmcp/manager.go` | Accept `[]string` MCP config paths,
dedup by name |
| `coderd/x/chatd/chatd.go` | Fetch config, thread through, named
returns |
| `coderd/x/chatd/instruction.go` | Accept configurable dir + file name,
`skillMetaFileFromParts` |
| `coderd/x/chatd/chattool/skill.go` | Accept configurable dirs + meta
file |
| `codersdk/chats.go` | `ContextFileSkillMetaFile` field for persistence
|

### Test coverage

- `TestConfig` (4 cases): defaults, custom env vars, whitespace
trimming, comma-separated dirs
- `TestResolvePath` / `TestResolvePaths`: including empty baseDir edge
case
- `TestPersistInstructionFilesFallbackOnOlderAgent`: backward-compat
path when `ContextConfig` returns 404
- `TestChatMessagePartVariantTags`: updated exclusion list for new
internal field

### Backward compatibility

Older agents return 404 for the new endpoint. `chatd` catches this and
falls back to today's defaults via `readHomeInstructionFile` (using
`LSRelativityHome`). Existing workspaces work with no changes.

</details>
This commit is contained in:
Kyle Carberry
2026-04-01 12:28:47 -04:00
committed by GitHub
parent b1c42bb630
commit ee855f9618
19 changed files with 1070 additions and 196 deletions
+15 -7
View File
@@ -38,6 +38,7 @@ import (
"cdr.dev/slog/v3"
"github.com/coder/clistat"
"github.com/coder/coder/v2/agent/agentcontainers"
"github.com/coder/coder/v2/agent/agentcontextconfig"
"github.com/coder/coder/v2/agent/agentexec"
"github.com/coder/coder/v2/agent/agentfiles"
"github.com/coder/coder/v2/agent/agentgit"
@@ -308,12 +309,13 @@ type agent struct {
containerAPI *agentcontainers.API
gitAPIOptions []agentgit.Option
filesAPI *agentfiles.API
gitAPI *agentgit.API
processAPI *agentproc.API
desktopAPI *agentdesktop.API
mcpManager *agentmcp.Manager
mcpAPI *agentmcp.API
filesAPI *agentfiles.API
gitAPI *agentgit.API
processAPI *agentproc.API
desktopAPI *agentdesktop.API
mcpManager *agentmcp.Manager
mcpAPI *agentmcp.API
contextConfigAPI *agentcontextconfig.API
socketServerEnabled bool
socketPath string
@@ -1263,6 +1265,12 @@ func (a *agent) handleManifest(manifestOK *checkpoint) func(ctx context.Context,
return xerrors.Errorf("update workspace agent startup: %w", err)
}
// Initialize the context config API with the expanded
// working directory so that it is ready before the HTTP
// handler is created (which happens after manifestOK).
a.contextConfigAPI = agentcontextconfig.NewAPI(
manifest.Directory,
)
oldManifest := a.manifest.Swap(&manifest)
manifestOK.complete(nil)
sentResult = true
@@ -1358,7 +1366,7 @@ func (a *agent) handleManifest(manifestOK *checkpoint) func(ctx context.Context,
// lifecycle transition to avoid delaying Ready.
// This runs inside the tracked goroutine so it
// is properly awaited on shutdown.
if mcpErr := a.mcpManager.Connect(a.gracefulCtx, manifest.Directory); mcpErr != nil {
if mcpErr := a.mcpManager.Connect(a.gracefulCtx, a.contextConfigAPI.Config().MCPConfigFiles); mcpErr != nil {
a.logger.Warn(ctx, "failed to connect to workspace MCP servers", slog.Error(mcpErr))
}
})
+83
View File
@@ -0,0 +1,83 @@
package agentcontextconfig
import (
"cmp"
"net/http"
"os"
"strings"
"github.com/go-chi/chi/v5"
"github.com/coder/coder/v2/coderd/httpapi"
"github.com/coder/coder/v2/codersdk/workspacesdk"
)
// Env var names for context configuration. Prefixed with EXP_
// to indicate these are experimental and may change.
const (
EnvInstructionsDirs = "CODER_AGENT_EXP_INSTRUCTIONS_DIRS"
EnvInstructionsFile = "CODER_AGENT_EXP_INSTRUCTIONS_FILE"
EnvSkillsDirs = "CODER_AGENT_EXP_SKILLS_DIRS"
EnvSkillMetaFile = "CODER_AGENT_EXP_SKILL_META_FILE"
EnvMCPConfigFiles = "CODER_AGENT_EXP_MCP_CONFIG_FILES"
)
// Defaults are defined in codersdk/workspacesdk so both
// the agent and server can reference them without a
// cross-layer import.
// API exposes the resolved context configuration through the
// agent's HTTP API.
type API struct {
config workspacesdk.ContextConfigResponse
}
// NewAPI reads context configuration from environment variables,
// resolves all paths relative to workingDir, and returns an API
// handler that serves the result.
func NewAPI(workingDir string) *API {
return &API{
config: Config(workingDir),
}
}
// Config reads env vars and resolves paths. Exported for use
// by the MCP manager and tests.
func Config(workingDir string) workspacesdk.ContextConfigResponse {
// TrimSpace all env vars before cmp.Or so that a
// whitespace-only value falls through to the default
// consistently. ResolvePaths also trims each comma-
// separated entry, but without pre-trimming here a
// bare " " would bypass cmp.Or and produce nil.
instructionsDir := cmp.Or(strings.TrimSpace(os.Getenv(EnvInstructionsDirs)), workspacesdk.DefaultInstructionsDir)
instructionsFile := cmp.Or(strings.TrimSpace(os.Getenv(EnvInstructionsFile)), workspacesdk.DefaultInstructionsFile)
skillsDir := cmp.Or(strings.TrimSpace(os.Getenv(EnvSkillsDirs)), workspacesdk.DefaultSkillsDir)
skillMetaFile := cmp.Or(strings.TrimSpace(os.Getenv(EnvSkillMetaFile)), workspacesdk.DefaultSkillMetaFile)
mcpConfigFile := cmp.Or(strings.TrimSpace(os.Getenv(EnvMCPConfigFiles)), workspacesdk.DefaultMCPConfigFile)
return workspacesdk.ContextConfigResponse{
InstructionsDirs: ResolvePaths(instructionsDir, workingDir),
InstructionsFile: instructionsFile,
SkillsDirs: ResolvePaths(skillsDir, workingDir),
SkillMetaFile: skillMetaFile,
MCPConfigFiles: ResolvePaths(mcpConfigFile, workingDir),
}
}
// Config returns the resolved config for use by other agent
// components (e.g. MCP manager).
func (api *API) Config() workspacesdk.ContextConfigResponse {
return api.config
}
// Routes returns the HTTP handler for the context config
// endpoint.
func (api *API) Routes() http.Handler {
r := chi.NewRouter()
r.Get("/", api.handleGet)
return r
}
func (api *API) handleGet(rw http.ResponseWriter, r *http.Request) {
httpapi.Write(r.Context(), rw, http.StatusOK, api.config)
}
+95
View File
@@ -0,0 +1,95 @@
package agentcontextconfig_test
import (
"path/filepath"
"testing"
"github.com/stretchr/testify/require"
"github.com/coder/coder/v2/agent/agentcontextconfig"
"github.com/coder/coder/v2/codersdk/workspacesdk"
)
func TestConfig(t *testing.T) {
t.Run("Defaults", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
// Clear all env vars so defaults are used.
t.Setenv(agentcontextconfig.EnvInstructionsDirs, "")
t.Setenv(agentcontextconfig.EnvInstructionsFile, "")
t.Setenv(agentcontextconfig.EnvSkillsDirs, "")
t.Setenv(agentcontextconfig.EnvSkillMetaFile, "")
t.Setenv(agentcontextconfig.EnvMCPConfigFiles, "")
workDir := platformAbsPath("work")
cfg := agentcontextconfig.Config(workDir)
require.Equal(t, workspacesdk.DefaultInstructionsFile, cfg.InstructionsFile)
require.Equal(t, workspacesdk.DefaultSkillMetaFile, cfg.SkillMetaFile)
// Default instructions dir is "~/.coder" which resolves
// to the home directory.
require.Equal(t, []string{filepath.Join(fakeHome, ".coder")}, cfg.InstructionsDirs)
// Default skills dir is ".agents/skills" (relative),
// resolved against the working directory.
require.Equal(t, []string{filepath.Join(workDir, ".agents", "skills")}, cfg.SkillsDirs)
// Default MCP config file is ".mcp.json" (relative),
// resolved against the working directory.
require.Equal(t, []string{filepath.Join(workDir, ".mcp.json")}, cfg.MCPConfigFiles)
})
t.Run("CustomEnvVars", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
optInstructions := platformAbsPath("opt", "instructions")
optSkills := platformAbsPath("opt", "skills")
optMCP := platformAbsPath("opt", "mcp.json")
t.Setenv(agentcontextconfig.EnvInstructionsDirs, optInstructions)
t.Setenv(agentcontextconfig.EnvInstructionsFile, "CUSTOM.md")
t.Setenv(agentcontextconfig.EnvSkillsDirs, optSkills)
t.Setenv(agentcontextconfig.EnvSkillMetaFile, "META.yaml")
t.Setenv(agentcontextconfig.EnvMCPConfigFiles, optMCP)
workDir := platformAbsPath("work")
cfg := agentcontextconfig.Config(workDir)
require.Equal(t, "CUSTOM.md", cfg.InstructionsFile)
require.Equal(t, "META.yaml", cfg.SkillMetaFile)
require.Equal(t, []string{optInstructions}, cfg.InstructionsDirs)
require.Equal(t, []string{optSkills}, cfg.SkillsDirs)
require.Equal(t, []string{optMCP}, cfg.MCPConfigFiles)
})
t.Run("WhitespaceInFileNames", func(t *testing.T) {
t.Setenv(agentcontextconfig.EnvInstructionsDirs, "")
t.Setenv(agentcontextconfig.EnvInstructionsFile, " CLAUDE.md ")
t.Setenv(agentcontextconfig.EnvSkillsDirs, "")
t.Setenv(agentcontextconfig.EnvSkillMetaFile, "")
t.Setenv(agentcontextconfig.EnvMCPConfigFiles, "")
workDir := platformAbsPath("work")
cfg := agentcontextconfig.Config(workDir)
require.Equal(t, "CLAUDE.md", cfg.InstructionsFile)
})
t.Run("CommaSeparatedDirs", func(t *testing.T) {
a := platformAbsPath("opt", "a")
b := platformAbsPath("opt", "b")
t.Setenv(agentcontextconfig.EnvInstructionsDirs, a+","+b)
t.Setenv(agentcontextconfig.EnvInstructionsFile, "")
t.Setenv(agentcontextconfig.EnvSkillsDirs, "")
t.Setenv(agentcontextconfig.EnvSkillMetaFile, "")
t.Setenv(agentcontextconfig.EnvMCPConfigFiles, "")
workDir := platformAbsPath("work")
cfg := agentcontextconfig.Config(workDir)
require.Equal(t, []string{a, b}, cfg.InstructionsDirs)
})
}
+55
View File
@@ -0,0 +1,55 @@
package agentcontextconfig
import (
"os"
"path/filepath"
"strings"
)
// ResolvePath resolves a single path that may be absolute,
// home-relative (~/ or ~), or relative to the given base
// directory. Returns an absolute path. Empty input returns empty.
func ResolvePath(raw, baseDir string) string {
raw = strings.TrimSpace(raw)
if raw == "" {
return ""
}
switch {
case raw == "~":
home, err := os.UserHomeDir()
if err != nil {
return ""
}
return home
case strings.HasPrefix(raw, "~/"):
home, err := os.UserHomeDir()
if err != nil {
return ""
}
return filepath.Join(home, raw[2:])
case filepath.IsAbs(raw):
return raw
default:
if baseDir == "" {
return ""
}
return filepath.Join(baseDir, raw)
}
}
// ResolvePaths splits a comma-separated list of paths and
// resolves each entry independently. Empty entries and entries
// that resolve to empty strings are skipped.
func ResolvePaths(raw, baseDir string) []string {
if strings.TrimSpace(raw) == "" {
return nil
}
parts := strings.Split(raw, ",")
out := make([]string, 0, len(parts))
for _, p := range parts {
if resolved := ResolvePath(p, baseDir); resolved != "" {
out = append(out, resolved)
}
}
return out
}
+152
View File
@@ -0,0 +1,152 @@
package agentcontextconfig_test
import (
"path/filepath"
"runtime"
"testing"
"github.com/stretchr/testify/require"
"github.com/coder/coder/v2/agent/agentcontextconfig"
)
// platformAbsPath constructs an absolute path that is valid
// on the current platform. On Windows paths must include a
// drive letter to be considered absolute.
func platformAbsPath(parts ...string) string {
if runtime.GOOS == "windows" {
return `C:\` + filepath.Join(parts...)
}
return "/" + filepath.Join(parts...)
}
func TestResolvePath(t *testing.T) { //nolint:tparallel // subtests using t.Setenv cannot be parallel
t.Run("EmptyInput", func(t *testing.T) {
t.Parallel()
require.Equal(t, "", agentcontextconfig.ResolvePath("", platformAbsPath("base")))
})
t.Run("WhitespaceOnly", func(t *testing.T) {
t.Parallel()
require.Equal(t, "", agentcontextconfig.ResolvePath(" ", platformAbsPath("base")))
})
// Tests that use t.Setenv cannot be parallel.
t.Run("TildeAlone", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
got := agentcontextconfig.ResolvePath("~", platformAbsPath("base"))
require.Equal(t, fakeHome, got)
})
t.Run("TildeSlashPath", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
got := agentcontextconfig.ResolvePath("~/docs/readme", platformAbsPath("base"))
require.Equal(t, filepath.Join(fakeHome, "docs", "readme"), got)
})
t.Run("AbsolutePath", func(t *testing.T) {
t.Parallel()
p := platformAbsPath("etc", "coder")
got := agentcontextconfig.ResolvePath(p, platformAbsPath("base"))
require.Equal(t, p, got)
})
t.Run("RelativePath", func(t *testing.T) {
t.Parallel()
base := platformAbsPath("work")
got := agentcontextconfig.ResolvePath("foo/bar", base)
require.Equal(t, filepath.Join(base, "foo", "bar"), got)
})
t.Run("RelativePathWithWhitespace", func(t *testing.T) {
t.Parallel()
base := platformAbsPath("work")
got := agentcontextconfig.ResolvePath(" foo/bar ", base)
require.Equal(t, filepath.Join(base, "foo", "bar"), got)
})
t.Run("RelativePathWithEmptyBaseDir", func(t *testing.T) {
t.Parallel()
got := agentcontextconfig.ResolvePath(".agents/skills", "")
require.Equal(t, "", got)
})
}
func TestResolvePath_HomeUnset(t *testing.T) {
// Cannot be parallel — modifies HOME env var.
t.Setenv("HOME", "")
// Also clear USERPROFILE for Windows compatibility.
t.Setenv("USERPROFILE", "")
require.Equal(t, "", agentcontextconfig.ResolvePath("~", platformAbsPath("base")))
require.Equal(t, "", agentcontextconfig.ResolvePath("~/docs", platformAbsPath("base")))
}
func TestResolvePaths(t *testing.T) { //nolint:tparallel // subtests using t.Setenv cannot be parallel
t.Run("EmptyString", func(t *testing.T) {
t.Parallel()
require.Nil(t, agentcontextconfig.ResolvePaths("", platformAbsPath("base")))
})
t.Run("WhitespaceOnly", func(t *testing.T) {
t.Parallel()
require.Nil(t, agentcontextconfig.ResolvePaths(" ", platformAbsPath("base")))
})
t.Run("SingleEntry", func(t *testing.T) {
t.Parallel()
p := platformAbsPath("abs", "path")
got := agentcontextconfig.ResolvePaths(p, platformAbsPath("base"))
require.Equal(t, []string{p}, got)
})
// Tests that use t.Setenv cannot be parallel.
t.Run("MultipleEntries", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
b := platformAbsPath("b")
base := platformAbsPath("base")
got := agentcontextconfig.ResolvePaths("~/a,"+b+",rel", base)
require.Equal(t, []string{
filepath.Join(fakeHome, "a"),
b,
filepath.Join(base, "rel"),
}, got)
})
t.Run("TrimsWhitespace", func(t *testing.T) {
t.Parallel()
a := platformAbsPath("a")
b := platformAbsPath("b")
got := agentcontextconfig.ResolvePaths(" "+a+" , "+b+" ", platformAbsPath("base"))
require.Equal(t, []string{a, b}, got)
})
t.Run("SkipsEmptyEntries", func(t *testing.T) {
t.Parallel()
a := platformAbsPath("a")
b := platformAbsPath("b")
got := agentcontextconfig.ResolvePaths(a+",,"+b+",", platformAbsPath("base"))
require.Equal(t, []string{a, b}, got)
})
t.Run("TrailingComma", func(t *testing.T) {
t.Parallel()
p := platformAbsPath("only")
got := agentcontextconfig.ResolvePaths(p+",", platformAbsPath("base"))
require.Equal(t, []string{p}, got)
})
t.Run("RelativePathSkippedWhenBaseDirEmpty", func(t *testing.T) {
fakeHome := t.TempDir()
t.Setenv("HOME", fakeHome)
t.Setenv("USERPROFILE", fakeHome)
got := agentcontextconfig.ResolvePaths("~/.coder,.agents/skills", "")
require.Equal(t, []string{filepath.Join(fakeHome, ".coder")}, got)
})
}
+1
View File
@@ -32,6 +32,7 @@ func (a *agent) apiHandler() http.Handler {
r.Mount("/api/v0/processes", a.processAPI.Routes())
r.Mount("/api/v0/desktop", a.desktopAPI.Routes())
r.Mount("/api/v0/mcp", a.mcpAPI.Routes())
r.Mount("/api/v0/context-config", a.contextConfigAPI.Routes())
if a.devcontainers {
r.Mount("/api/v0/containers", a.containerAPI.Routes())
+34 -11
View File
@@ -6,7 +6,6 @@ import (
"fmt"
"io/fs"
"os"
"path/filepath"
"slices"
"strings"
"sync"
@@ -70,16 +69,40 @@ func NewManager(logger slog.Logger) *Manager {
}
}
// Connect discovers .mcp.json in dir and connects to all
// configured servers. Failed servers are logged and skipped.
func (m *Manager) Connect(ctx context.Context, dir string) error {
path := filepath.Join(dir, ".mcp.json")
configs, err := ParseConfig(path)
if err != nil {
if errors.Is(err, fs.ErrNotExist) {
return nil
// Connect reads MCP config files at the given absolute paths and
// connects to all configured servers. Failed servers are logged
// and skipped. Missing config files are silently skipped.
func (m *Manager) Connect(ctx context.Context, mcpConfigFiles []string) error {
var allConfigs []ServerConfig
for _, configPath := range mcpConfigFiles {
configs, err := ParseConfig(configPath)
if err != nil {
if errors.Is(err, fs.ErrNotExist) {
continue
}
m.logger.Warn(ctx, "failed to parse MCP config",
slog.F("path", configPath),
slog.Error(err),
)
continue
}
return xerrors.Errorf("parse mcp config: %w", err)
allConfigs = append(allConfigs, configs...)
}
// Deduplicate by server name; first occurrence wins.
seen := make(map[string]struct{})
deduped := make([]ServerConfig, 0, len(allConfigs))
for _, cfg := range allConfigs {
if _, ok := seen[cfg.Name]; ok {
continue
}
seen[cfg.Name] = struct{}{}
deduped = append(deduped, cfg)
}
allConfigs = deduped
if len(allConfigs) == 0 {
return nil
}
// Connect to servers in parallel without holding the
@@ -95,7 +118,7 @@ func (m *Manager) Connect(ctx context.Context, dir string) error {
connected []connectedServer
)
var eg errgroup.Group
for _, cfg := range configs {
for _, cfg := range allConfigs {
eg.Go(func() error {
c, err := m.connectServer(ctx, cfg)
if err != nil {