Context files (AGENTS.md) and skills were only fetched from the
workspace on the first turn or when the agent changed. On subsequent
turns, stale content from persisted messages was used. This meant that
if AGENTS.md or skills were modified on the workspace between turns, the
agent wouldn't see the changes until the user created a new chat.
## Changes
- Extract `fetchWorkspaceContext` from `persistInstructionFiles` to
allow fetching workspace context without persisting
- On subsequent turns, re-fetch fresh context from the workspace instead
of reading stale persisted content; falls back to persisted messages if
the workspace dial fails
- Update `ReloadMessages` callback to re-derive instruction and skills
from reloaded database messages after compaction, instead of using
captured closure variables
- Add `formatSystemInstructionsFromParts` helper to build system
instructions directly from agent parts without requiring separate
OS/directory params
- Add tests for the new helper
<details><summary>Implementation Notes</summary>
### Root cause
In `runChat`, the `else if hasContextFiles` branch (subsequent turns)
called `instructionFromContextFiles(messages)` which read stale content
from persisted DB messages. The `ReloadMessages` callback
(post-compaction) also used captured `instruction`/`skills` closure
variables from the start of the turn, never re-deriving them.
### Approach
1. **Extract `fetchWorkspaceContext`** — Pure refactor of the fetch-only
part of `persistInstructionFiles` (agent connection, context config
retrieval, content sanitization, metadata stamping). Returns parts +
skills without persisting.
2. **Subsequent turns**: Instead of reading from persisted messages,
launch a `g2` goroutine that calls `fetchWorkspaceContext` to get fresh
context from the workspace. Falls back gracefully to persisted messages
if the workspace is unreachable.
3. **ReloadMessages**: Re-derive `instruction` from
`instructionFromContextFiles(reloadedMsgs)` and `skills` from
`skillsFromParts(reloadedMsgs)` using the freshly loaded messages, with
fallback to captured values if the reloaded messages don't contain
context (e.g. compacted away).
</details>
> 🤖 Generated by Coder Agents
> This PR was authored by Mux on behalf of Mike.
Chats sharing one workspace (e.g. sibling subagents) all wrote to
`/home/coder/PLAN.md`, causing plan file collisions. This change derives
a unique plan path per chat from the workspace home directory and chat
ID.
## Changes
* `write_file`, `edit_files`, and `propose_plan` reject any `plan.md`
variant (case-insensitive) at the workspace home root, with a clear
error pointing to the chat-specific path.
* Root chats receive a `<plan-file-path>` block inlined in the main
system prompt with the concrete path.
* Prompt and tool descriptions no longer hardcode `/home/coder/PLAN.md`.
* Plan path handling is POSIX-only (forward-slash), relying on the
contract that workspace agent paths are normalized before reaching
chatd.
* Updated `ProposePlanTool.stories.tsx` to use per-chat path examples.
* Full test coverage for plan path detection, legacy-path rejection in
all three tools, inline prompt rendering, and fallback behavior.
Piggybacks on #23878. Moves instruction file reading and skill discovery
from `chatd` (server-side, via multiple `LS`/`ReadFile` round-trips
through the agent connection) to the agent itself (local filesystem
access).
This intentionally drops backward compatibility with older agents that
don't support the context-config endpoint. Agents and server are
deployed together; there is no rolling-update contract to maintain here.
## What changed
The agent's `GET /api/v0/context-config` response now returns
`[]ChatMessagePart` directly — the same types chatd persists. This
eliminates intermediate type conversions and makes the protocol
extensible.
| Field | Type | Description |
|---|---|---|
| `parts` | `[]ChatMessagePart` | Context-file and skill parts, ready to
persist |
| `working_dir` | `string` | Agent's resolved working directory |
Removed from the response: `instructions_dirs`, `instructions_file`,
`skills_dirs`, `skill_meta_file`, `mcp_config_files` — the agent reads
files locally and returns their content as parts.
Removed from chatd: all legacy `LS`/`ReadFile` fallback code
(`readHomeInstructionFile`, `readInstructionDirFile`, `DiscoverSkills`
via LS, etc).
## Why
The previous architecture had the agent resolve paths, serve them over
HTTP, then `chatd` make N+1 round-trips back through the agent
connection to read files. The agent has direct filesystem access and
should just read the files.
## Key design decisions
- **Agent returns `ChatMessagePart` directly** — same types chatd
persists. No intermediate `InstructionFileEntry`/`SkillEntry` types
needed.
- **`SkillMeta.MetaFile`** — persisted via `ContextFileSkillMetaFile` on
the skill part, so custom meta file names
(`CODER_AGENT_EXP_SKILL_META_FILE`) survive across chat turns.
- **No pre-read body** — `read_skill` always dials the workspace to
fetch the skill body on demand. Simpler than caching the body in the
response.
- **MCP config paths kept agent-internal** — `MCPConfigFiles()` getter,
not sent over the wire.
- **No backward compat fallback** — old agents that don't support
context-config get no instruction files. This is acceptable since agent
and server deploy together.
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>
- Add `SanitizePromptText` stripping ~24 invisible Unicode codepoints
and collapsing excessive newlines
- Apply at write and read paths for defense-in-depth
- Frontend: warn in both prompt textareas when invisible characters
detected
- Explicit codepoint list (not blanket `unicode.Cf`) to avoid breaking
flag emoji
- 34 Go tests + idempotency meta-test, 11 TS unit tests, 4 Storybook
stories
> This PR was created with the help of Coder Agents, and was reviewed by my human.
- Moves `coderd/chatd/`, `coderd/gitsync/`, `enterprise/coderd/chatd/`
under `x/` parent directories to signal instability
- Adds `Experimental:` glue code comments in `coderd/coderd.go`
> 🤖 This PR was created with the help of Coder Agents, and was
reviewed by my human. 🧑💻
Kyle Carberry