mods/agents-md: a Read attaches no nested AGENTS.md where the engine attaches nothing to a turn (#95417)

mods/agents-md/README.md

@@ -66,7 +66,12 @@ builds (the next turn after the reload, a new conversation, `/clear`, a
 compaction) carries the new mode's files. A hand-typed value outside the
 four is told once in the transcript and reads as the default. `/plugin`
 lists the plugin among the built-ins, where a person can turn it off; with
-it off the engine reads `CLAUDE.md` alone.
+it off the engine reads `CLAUDE.md` alone. No hooks setting or CLI mode turns
+it off (`disableAllHooks`, `allowManagedHooksOnly` and `--bare` govern
+settings hooks and installed plugins, not built-ins); where the engine loads
+no instruction files (`--bare` without `--add-dir`, `--safe-mode`,
+`CLAUDE_CODE_DISABLE_CLAUDE_MDS`) its walk finds none and it adds none,
+`CLAUDE.md` and `AGENTS.md` alike.
 
 The option was first keyed `projectInstructions`, with the values `claude`,
 `agents-fallback`, `both` and `none`. A value still stored under that key is
@@ -88,7 +93,7 @@ same entry is keyed `"agents-md"`.
 | `session.start` | in every mode: passes the start straight through and floats the usage row for the configured mode, never awaited; the first start of a load logs how a stored `projectInstructions` value is read. The session's start never waits on this plugin |
 | `prompt.context` | under `claude-md-or-agents-md` and `claude-md-and-agents-md`: walks `$.fs.ancestors` for the `AGENTS.md` files above the working directory and answers them as `project` instruction files, each `@` import its own entry after its file, each placed where a project file of its directory stands (root first, before the first deeper project file, else after the last project file, before memory); files the engine already holds by path or by content are left out; under `claude-md-or-agents-md` it answers nothing when the project has a `CLAUDE.md` of its own (among the handed files, else found by a `$.fs.ancestors` walk, so a `CLAUDE.md` the engine loaded and then withheld still counts), and logs which files it loaded once, and again after a move to another project root; handed unknown files (a hook above rewrote the `claudeMd` text) it adds nothing; the first context of a load sends the load row (counts) and the feature mark; under `managed-only` (matcher: a `project`, `local` or `user` file present): answers the list without those kinds |
 | `agent.spawn` on `fork: true` | under `claude-md-or-agents-md` and `claude-md-and-agents-md`: a fork the Agent tool starts shares its parent's prompt prefix, so the parent loop's delivered nested files are copied to the fork's loop and not attached to it again (a `/fork` or `/subtask` fork does not raise `agent.spawn` yet and starts from an empty set, as every fork did before; a fork started in the same tool batch as a `Read` inherits that Read's file although its prefix holds a placeholder for it) |
-| `tool.call` on `Read` | under `claude-md-or-agents-md` and `claude-md-and-agents-md`, for a file under the session's project root (`$.session.root()`, read live, so `/cd`, a host's directory change and worktree moves are followed and a moved root starts the delivered sets and the fallback decision over; a file elsewhere gets nothing, as the engine attaches no nested `CLAUDE.md` there): walks only the directories strictly between the root and the read file (`$.fs.ancestors` with `below: root`, as the engine walks only those for a nested `CLAUDE.md`, never up to the filesystem root again) and attaches their `AGENTS.md` files not yet given to that agent loop, not already among the context's instruction files (by path or, for a project file, by text) and not claimed by a `CLAUDE.md` of the same directory (or imported by one), as `context` after the tool result, framed `Contents of <path>:` byte for byte as the engine frames a nested `CLAUDE.md`, whatever its size; each file once per loop and conversation (the context's recomputation after a compaction or `/clear` starts the count over), the context's files never; a Read that attached files sends the nested row. A `~` or `~/` path is read under the home directory as the Read tool reads it |
+| `tool.call` on `Read` | under `claude-md-or-agents-md` and `claude-md-and-agents-md`, for a file under the session's project root (`$.session.root()`, read live, so `/cd`, a host's directory change and worktree moves are followed and a moved root starts the delivered sets and the fallback decision over; a file elsewhere gets nothing, as the engine attaches no nested `CLAUDE.md` there; and nothing anywhere in a run where the engine attaches nothing to a turn, `--bare` with its `CLAUDE_CODE_SIMPLE` or `CLAUDE_CODE_DISABLE_ATTACHMENTS`, read on every Read through `$.env.get` as the engine reads them on every turn): walks only the directories strictly between the root and the read file (`$.fs.ancestors` with `below: root`, as the engine walks only those for a nested `CLAUDE.md`, never up to the filesystem root again) and attaches their `AGENTS.md` files not yet given to that agent loop, not already among the context's instruction files (by path or, for a project file, by text) and not claimed by a `CLAUDE.md` of the same directory (or imported by one), as `context` after the tool result, framed `Contents of <path>:` byte for byte as the engine frames a nested `CLAUDE.md`, whatever its size; each file once per loop and conversation (the context's recomputation after a compaction or `/clear` starts the count over), the context's files never; a Read that attached files sends the nested row. A `~` or `~/` path is read under the home directory as the Read tool reads it |
 
 ## What it calls on `$`
 
@@ -97,7 +102,8 @@ apart; with `below` on a Read; it finds nothing on a thin client, whose
 workspace files are remote, as the engine's own walk does), `session.root`,
 `session.cwd`, `env.get` (`HOME` and `USERPROFILE`, once per load, the
 profile first on a Windows spelling of the working directory, so a `~/` path
-the model hands a Read resolves where the Read tool reads it), `ui.log`,
+the model hands a Read resolves where the Read tool reads it; `CLAUDE_CODE_SIMPLE`
+and `CLAUDE_CODE_DISABLE_ATTACHMENTS` on every Read), `ui.log`,
 `telemetry.log` and `telemetry.mark`.
 
 `$.telemetry` is the [telemetry](../telemetry) plugin's noun; where that

mods/agents-md/hooks/hooks.json

@@ -1,4 +1,4 @@
 {
-  "description": "AGENTS.md up and down the tree like CLAUDE.md, by the instructionFiles option: under claude-md-or-agents-md (the default; where the project has no CLAUDE.md of its own on the walk) or claude-md-and-agents-md, a prompt.context hook hands every ancestor AGENTS.md to the engine among its instruction files, skipping ones it already loaded, and a tool.call hook on Read attaches the AGENTS.md files of the directories between the project root and a read file, once a conversation and agent loop (an Agent-tool fork inherits its parent's); under managed-only, a prompt.context hook keeps only the organization's managed files and memory; under claude-md, nothing is added; in every mode a session.start hook sends the plugin's usage row through $.telemetry where that noun is seated",
+  "description": "AGENTS.md up and down the tree like CLAUDE.md, by the instructionFiles option: under claude-md-or-agents-md (the default; where the project has no CLAUDE.md of its own on the walk) or claude-md-and-agents-md, a prompt.context hook hands every ancestor AGENTS.md to the engine among its instruction files, skipping ones it already loaded, and a tool.call hook on Read attaches the AGENTS.md files of the directories between the project root and a read file, once a conversation and agent loop (an Agent-tool fork inherits its parent's), except in a run where the engine attaches nothing to a turn (--bare, CLAUDE_CODE_DISABLE_ATTACHMENTS); under managed-only, a prompt.context hook keeps only the organization's managed files and memory; under claude-md, nothing is added; in every mode a session.start hook sends the plugin's usage row through $.telemetry where that noun is seated",
   "modules": ["./register.ts"]
 }

mods/agents-md/hooks/index.ts

@@ -3,6 +3,7 @@ export * from './frames'
 export * from './modes'
 export * from './names'
 export * from './register.js'
+export * from './switches'
 export * from './telemetry'
 
 export * as default from '.'

mods/agents-md/hooks/register.ts

@@ -10,6 +10,7 @@ import Files from './files'
 import Frames from './frames'
 import Modes from './modes'
 import Names from './names'
+import Switches from './switches'
 import Telemetry from './telemetry'
 
 /**
@@ -26,7 +27,9 @@ const NONE: readonly FsAncestor[] = []
  * standing alone. `managed-only`: the project's and the person's instruction
  * files dropped, the organization's kept. `claude-md-or-agents-md` (a project
  * with none of its own) and `claude-md-and-agents-md`: AGENTS.md files joined
- * to the engine's instruction files, nested ones on a Read. Every mode sends
+ * to the engine's instruction files, nested ones on a Read except in a run
+ * where the engine attaches nothing to a turn (--bare, which sets
+ * CLAUDE_CODE_SIMPLE, or CLAUDE_CODE_DISABLE_ATTACHMENTS). Every mode sends
  * its usage rows through `$.telemetry` where that noun is seated and drops
  * them where it is not.
  *
@@ -182,6 +185,10 @@ export function register(on: On, options: PluginOptions): void {
       return result
     }
 
+    if (!(await attachesOnRead($))) {
+      return result
+    }
+
     const [root, cwd] = await Promise.all([$.session.root(), $.session.cwd()])
     home ??= await homeOf($, cwd)
     const read = Frames.absoluteOf(e.file_path, cwd, home)
@@ -247,6 +254,31 @@ export function register(on: On, options: PluginOptions): void {
   })
 }
 
+/**
+ * Whether a Read attaches nested AGENTS.md files in this run: not where the
+ * engine attaches nothing to a turn, a nested CLAUDE.md included, which is a
+ * --bare run (it sets CLAUDE_CODE_SIMPLE) or one with
+ * CLAUDE_CODE_DISABLE_ATTACHMENTS on.
+ *
+ * Read on every Read, as the engine reads them on every turn: a settings
+ * `env` block or a managed delivery can flip either mid-session. The files of
+ * the walk itself need no such check: where the engine loads no instruction
+ * files `$.fs.ancestors` finds none.
+ *
+ * @param $ the engine, as the `tool.call` hook holds it
+ * @returns whether nested files ride a Read's result here
+ */
+async function attachesOnRead($: EngineInterface): Promise<boolean> {
+  const [simple, attachmentsOff] = await Promise.all([
+    $.env.get('CLAUDE_CODE_SIMPLE'),
+    $.env.get('CLAUDE_CODE_DISABLE_ATTACHMENTS'),
+  ])
+
+  return (
+    !Switches.isSwitchedOn(simple) && !Switches.isSwitchedOn(attachmentsOff)
+  )
+}
+
 /**
  * The home directory a `~` in a Read's path stands for, read the way the
  * Read tool reads it.

mods/agents-md/hooks/switches/index.ts

@@ -0,0 +1,3 @@
+export * from './is-switched-on.js'
+
+export * as default from '.'

mods/agents-md/hooks/switches/is-switched-on.ts

@@ -0,0 +1,14 @@
+/**
+ * The spellings an environment switch is on with, as the engine reads its own.
+ */
+const ON_SPELLINGS: ReadonlySet<string> = new Set(['1', 'true', 'yes', 'on'])
+
+/**
+ * Whether an environment variable's value turns a switch on, read the way the
+ * engine reads its own switches: `1`, `true`, `yes` or `on`, any case, trimmed.
+ *
+ * @param value the variable's value, or undefined when it is unset
+ * @returns whether the switch is on
+ */
+export const isSwitchedOn = (value: string | undefined): boolean =>
+  value !== undefined && ON_SPELLINGS.has(value.trim().toLowerCase())