diff --git a/docs/core-data-structures/bash.md b/docs/core-data-structures/bash.md
index 807c7401fc..273ba5ebe8 100644
--- a/docs/core-data-structures/bash.md
+++ b/docs/core-data-structures/bash.md
@@ -17,6 +17,24 @@ interface BashExecRequest {
   timeoutMs?: number | undefined
   /** Abort signal — implementations kill the command when it fires. */
   signal?: AbortSignal | undefined
+  /**
+   * Bytes to write to the command's stdin, then close it. Absent leaves stdin
+   * closed/empty (the default for model-driven tool calls). Set by in-process
+   * plugins (e.g. the hooks bridges, which write a hook command's JSON payload
+   * to its stdin); the model-facing bash tool does not expose it as a parameter
+   * (a model that needs stdin uses shell syntax like a heredoc or a pipe).
+   */
+  stdin?: string | undefined
+  /**
+   * Extra environment entries for the command, merged AFTER the
+   * implementation's credential scrub (so an explicit entry here is honored even
+   * when its name matches the scrub pattern — the caller named a value it holds,
+   * not the harness's ambient secret). Set by in-process plugins (the hooks
+   * bridges set `CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, …); the model-facing
+   * bash tool does not expose it as a parameter (a model that needs an env var
+   * uses shell syntax like `FOO=bar cmd`).
+   */
+  env?: Record<string, string> | undefined
   /**
    * Opaque OWNER token for a background task — the consumer's isolation key
    * (the tool layer passes the owning agent's `session.header.id`). The
@@ -36,6 +54,22 @@ interface BashExecSpec {
   timeoutMs: number
   /** Abort signal — implementations kill the command when it fires. */
   signal?: AbortSignal | undefined
+  /**
+   * Bytes to write to the command's stdin (then close it), carried through
+   * verbatim from {@link BashExecRequest.stdin}. OPTIONAL on the resolved spec
+   * (unlike `owner`): it has no config default, so a missing one means "no
+   * stdin" — the safe, ordinary case — not a silent footgun, so it stays a
+   * plain optional rather than required-but-nullable (see the request field).
+   */
+  stdin?: string | undefined
+  /**
+   * Extra environment entries, carried through verbatim from
+   * {@link BashExecRequest.env} and merged by the implementation AFTER its
+   * credential scrub (an explicit entry wins even when its name matches the
+   * scrub pattern). OPTIONAL on the spec for the same reason as `stdin` — no
+   * config default, absent means "no extra env".
+   */
+  env?: Record<string, string> | undefined
   /**
    * Opaque owner token, REQUIRED-but-nullable (mirrors `workdir`/`timeoutMs`
    * being required on the resolved spec): {@link BashExecutor.resolve} carries
@@ -50,6 +84,8 @@ interface BashExecSpec {
 
 The `owner` token is the isolation key: the executor stores it but never interprets it (access policy is the consumer's job), so a background task started by one agent isn't readable cross-session. A required-but-nullable field makes a forgotten owner a visible `undefined` rather than a silently-unowned task.
 
+`stdin` and `env` are set by in-process plugins (the hooks bridges, native plugins) to feed a hook command its JSON payload on stdin and its `CLAUDE_PROJECT_DIR`/`CLAUDE_PLUGIN_ROOT` env. The model-facing `dsh-tool-bash` tool does not expose them as parameters — its request is built from `command`/`workdir`/`timeoutMs`/`signal`/`owner` only — because a model already has equivalent power through shell syntax (`FOO=bar cmd`, a heredoc), so duplicating them as tool params would be redundant. This is NOT a security boundary: the credential scrub in `dsh-bash-local` is what stops the harness's ambient secrets reaching a spawned command, and it works regardless of these fields (a model cannot read a value the scrub removed, and tool-call args are static JSON, never shell-evaluated). A guard test asserts the tool doesn't forward model `env`/`stdin` — to catch a future `...args` spread, not to defend a trust wall. `env` is merged AFTER the scrub so an explicit caller entry (a value it already holds) wins even on a credential-shaped name. See [the bash-stdin-env RFC](../rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
+
 Both ids the seam handles are [branded](core.md) (zero-cost `string` brands, the same machinery as `SessionId`/`AgentId`): `BashTaskId` (a tracked background task, generated `bash-N` by the local executor) and `OwnerToken` (the opaque isolation key). `OwnerToken` is deliberately a DISTINCT brand from `SessionId`, not an alias: the bash seam is a capability seam that must not know what an owner token *means*, so it never imports `dsh-session`'s vocabulary — the `dsh-tool-bash` consumer is the single boundary that casts the owning agent's `SessionId` into an `OwnerToken`. Branding both stops a raw `string` (or a `BashTaskId` where an `OwnerToken` is expected, or vice versa) from slipping through the type checker on the model-facing `task_id` path.
 
 ## Foreground runs: `BashRunResult`
diff --git a/docs/rfc/README.md b/docs/rfc/README.md
index 9928a5f125..ed6bd08fa0 100644
--- a/docs/rfc/README.md
+++ b/docs/rfc/README.md
@@ -126,6 +126,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
 | [Web capability seam — provider registry and model-facing web tools](implemented/architecture/2026-06-24-web-capability-seam.md) | 2026-06-24 |
 | [Make `dsh-fs-policy` an event-gate plugin, not a method interface](implemented/architecture/2026-06-26-file-context-as-event-gate.md) | 2026-06-26 |
 | [Event-domain semantics — session is the fact log, agent is the live surface](implemented/architecture/2026-06-30-event-domain-semantics.md) | 2026-06-30 |
+| [stdin + extra env on the bash seam](implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md) | 2026-06-30 |
 | [Resolve filesystem paths against the caller's session cwd](implemented/architecture/2026-07-02-fs-per-session-cwd.md) | 2026-07-02 |
 | [Tagged render-intent union for tool-call presentation](implemented/architecture/2026-07-02-tool-render-intent-union.md) | 2026-07-02 |
 | [Result-time applied-hunk diffs for file mutations](implemented/architecture/2026-07-02-result-time-applied-hunk-diffs.md) | 2026-07-02 |
diff --git a/docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md b/docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md
new file mode 100644
index 0000000000..cda9f00e9e
--- /dev/null
+++ b/docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md
@@ -0,0 +1,33 @@
+# RFC: stdin + extra env on the bash seam
+
+Status: implemented (accepted 2026-06-30)
+
+<!-- XXX: legacy ADR/RFC body format, not yet normalized to a unified RFC template. -->
+
+## Context
+
+The hooks subsystem runs external hook commands the way Claude Code and Codex do: a hook is a shell command that receives its event payload as **JSON on stdin** and reads context from a handful of **environment variables** (`CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, `PLUGIN_ROOT`, …). The harness already has a perfectly good command runner behind the `ctx.bash` capability seam ([dsh-bash](../../../../packages/bash/bash) → [dsh-bash-local](../../../../packages/bash/bash-local)), with process-group kills, output truncation/spill, and a credential scrub. Reusing it for hook execution means a hook bridge does not re-implement subprocess plumbing — but the seam had no way to write stdin or set extra env. This RFC adds those two inputs.
+
+**These fields are NOT a new security boundary.** It is tempting to frame arbitrary-stdin / arbitrary-env as "dangerous, so gate who may use them" — but that framing is wrong, because a model driving the `bash` tool **already** has equivalent power through ordinary shell syntax: `FOO=bar cmd` sets an env var, a heredoc or `printf … | cmd` feeds arbitrary stdin. Adding `env`/`stdin` as seam fields grants the model no capability it lacks. In particular they cannot exfiltrate the harness's ambient credentials: the real control for that is the **credential scrub** in [dsh-bash-local](../../../../packages/bash/bash-local)'s `childEnv()`, which strips `*KEY*`/`*SECRET*`/`*TOKEN*` from `process.env` before the child sees it (see [AGENTS.md](../../../../AGENTS.md) § Defensive patterns, "Never hand untrusted/model output the ambient environment or predictable paths"). The scrub works regardless of these fields — a model cannot read a value that is not in the environment, and tool-call arguments are static JSON, never shell-evaluated, so a model cannot write `env: {LEAK: $DEEPSEEK_API_KEY}` and have it expand. So the security question is already answered by the scrub; this RFC is only about giving trusted in-process callers a clean way to pass a JSON payload + `CLAUDE_*` vars without routing them through model-visible shell text.
+
+## Decision
+
+Add `stdin?: string` and `env?: Record<string, string>` to **both** `BashExecRequest` (the model-/plugin-facing request) and `BashExecSpec` (the resolved spec `run`/`start` act on), and thread them through `dsh-bash-local`: `resolve()` carries them verbatim, `run()`/`start()` pass them to `runBash`, which writes the bytes to the child's stdin and merges the extra env.
+
+Three deliberate choices:
+
+1. **The model-facing `bash` tool simply does NOT expose `stdin`/`env` as parameters** — not as a security wall, but because bash syntax already covers the model's needs, so duplicating them as tool params would be redundant surface. [dsh-tool-bash](../../../../packages/bash/tool-bash)'s `bash` tool builds its `BashExecRequest` from `command`/`workdir`/`timeoutMs`/`signal`/`owner` only; a model that includes `env`/`stdin` keys in its tool-call arguments simply has them ignored. A regression guard (`tool-bash` "does not forward env/stdin" tests) drives the real tool with those extra args and asserts the recorded request carries neither field — its purpose is to catch a future refactor that blindly spreads `...args` into the request and silently starts forwarding model input into the post-scrub `env` merge, NOT to defend a trust boundary. In-process plugins (the hooks bridges, native plugins) that construct a `BashExecRequest` directly set the fields; the seam imposes no access policy (consistent with how `owner` works — the executor stores but never interprets it).
+
+2. **`env` merges AFTER the credential scrub, so an explicit caller entry always wins** — even a credential-shaped name. This is correct because the scrub's job is narrow: stop the harness's *ambient* `process.env` credentials from leaking into a spawned command. A caller that explicitly sets a var has named a value it already holds (not the ambient secret), so the scrub is not a constraint on it. `childEnv(extra?)` layers `scrub(process.env)` → `ENV_OVERRIDES` (the model-friendly `TERM=dumb` etc.) → `extra`, last-wins.
+
+3. **`stdin`/`env` are required-absent-OK (plain optional) on the resolved spec, NOT required-but-nullable like `owner`.** `owner` is required-but-nullable because a *silently* missing owner yields an unowned, cross-session-readable task — a security footgun that a visible `undefined` guards against. `stdin`/`env` have no such hazard: a missing one means "no stdin / no extra env", which is the safe, ordinary case (every model-driven call). So they stay plain optionals, matching `signal`.
+
+`dsh-bash-local` spawns stdin as a `'pipe'` (writing the supplied bytes, then closing) ONLY when a caller set `stdin`; with none supplied it uses `'ignore'` — fd 0 → `/dev/null` — the exact pre-seam default. This distinction is observable and deliberate: a closed empty pipe and `/dev/null` are NOT the same file type (node's spawn pipe is an `AF_UNIX` socket, so `test -c /dev/stdin` holds for `/dev/null` but not for an empty pipe), so the no-stdin path — every model-driven call — must keep `/dev/null` rather than regress to an always-open pipe. Each branch's `stdio` tuple is a literal, which preserves the typed `spawn` overload that guarantees non-null `stdout`/`stderr`. When stdin IS written, a child that exits without reading makes the write fail EPIPE; that error is swallowed (the command's outcome rides on its exit code/output, not the write) so it never crashes the host or rejects `done`.
+
+## Scope: configurable scrub pattern is NOT included
+
+An earlier sketch of this work also proposed making `SENSITIVE_ENV_PATTERN` configurable. Validating against the code, that is **speculative and already subsumed**: `run.ts` documents a configurable whitelist as future work, and the new explicit `env` field — merged after the scrub — already gives a caller full control, including over credential-shaped vars. There is no current caller that needs to *broaden* the ambient scrub (the hazard runs the other way). Adding a config knob now would be a feature with no consumer, against [AGENTS.md](../../../../AGENTS.md) § "Don't add features beyond what the task requires". If a real workflow ever needs to forward a specific ambient credential, the explicit `env` field is the supported path; a configurable scrub can be reconsidered then.
+
+## Consequences
+
+A hook bridge builds a `BashExecRequest` with the hook's JSON payload as `stdin` and its `CLAUDE_*`/`PLUGIN_ROOT` vars as `env`, and runs it through the same `ctx.bash` everything else uses — no bespoke subprocess code, and the full process-group-kill / truncation / spill machinery for free. The model-facing attack surface is unchanged (the credential scrub, not these fields, is what bounds it), and the `bash` tool's request-building stays the single place that decides which fields a model call carries — guarded by a test that fails if a refactor starts forwarding model input. The vocabulary addition is documented in [docs/core-data-structures/bash.md](../../../core-data-structures/bash.md) (the `type-equiv` request/spec blocks) and the three bash-package READMEs.
diff --git a/packages/bash/bash-local/README.md b/packages/bash/bash-local/README.md
index 016f57d2a9..e6ecc25cac 100644
--- a/packages/bash/bash-local/README.md
+++ b/packages/bash/bash-local/README.md
@@ -21,7 +21,7 @@ Design surveyed against the bash tools of Claude Code, OpenCode, Codex, and pi;
 - **Spawn per call, no shell state** — every call is a fresh non-login `bash -c` (deterministic; no rc files). All four surveyed tools spawn per call. `XXX(stateful-shell)` in `src/run.ts` records the two proven stateful designs (Claude Code's cwd-only persistence; Codex's PTY exec sessions) for when real workflows demand them.
 - **Process-group kills with escalation** — children are spawned `detached` (own process group); kills send SIGTERM to the group, then SIGKILL after a 3s grace (OpenCode's escalation; pipelines and subshells die with the parent). ESRCH is tolerated; daemons that re-parent away from the group can still survive — same caveat as the surveyed tools.
 - **Tail-keep truncation + spill files** — output beyond `maxOutputBytes` keeps the in-memory TAIL (errors/results cluster at the end — pi/OpenCode rationale) while the FULL stream is appended to a temp file whose path is reported when available. If the final spill close reports a delayed writeback failure, the executor still returns the tail but withholds the path rather than advertising a possibly incomplete file.
-- **Model-friendly env** — `NO_COLOR=1 TERM=dumb PAGER=cat GIT_PAGER=cat` (Codex's hardcoded set) so pagers and ANSI color don't garble results.
+- **Model-friendly env + credential scrub** — `process.env` minus credential-shaped vars (`*KEY*`/`*SECRET*`/`*TOKEN*`), then `NO_COLOR=1 TERM=dumb PAGER=cat GIT_PAGER=cat` (Codex's hardcoded set) so pagers and ANSI color don't garble results. This scrub is the security control that keeps the harness's *ambient* credentials out of a spawned command. A spec's `env` is merged LAST (after the scrub), so a caller's explicit entry — a value it already holds — wins even on a credential-shaped name. The spec's `stdin`, when supplied, is written to the child and closed; with none supplied, fd 0 is `/dev/null` — the exact pre-seam default, so a command that probes stdin's file type is unaffected. Both `env`/`stdin` are set by in-process plugins (the hooks bridges); the model-facing tool doesn't expose them. See [the bash-stdin-env RFC](../../../docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
 - **Background tasks** — `start()` returns immediately, no timeout applies (Claude Code detaches timeouts when backgrounding), `readOutput()` is incremental with whole-stream byte offsets, and disposal kills everything. The spec's opaque `owner` token is stored on the tracked task and returned by `ownerOf(id)` — the executor never interprets it (the consumer's access policy does), and because it lives with the task here it survives a `tool-bash` HMR reload.
 
 ## Sandboxing
diff --git a/packages/bash/bash-local/src/index.ts b/packages/bash/bash-local/src/index.ts
index 05f1ed75dd..b1ea729fb4 100644
--- a/packages/bash/bash-local/src/index.ts
+++ b/packages/bash/bash-local/src/index.ts
@@ -116,6 +116,10 @@ export class LocalBashExecutor extends BashExecutor {
       workdir: request.workdir ?? this.config.cwd ?? process.cwd(),
       timeoutMs,
       ...request.signal ? { signal: request.signal } : {},
+      // Carry stdin/env through verbatim — optional, no config default (absent
+      // means none). env merges AFTER the scrub in run.ts.
+      ...request.stdin !== undefined ? { stdin: request.stdin } : {},
+      ...request.env !== undefined ? { env: request.env } : {},
       // Carry the owner through verbatim (required-but-nullable on the spec):
       // the executor never interprets it — the consumer's access policy does.
       owner: request.owner,
@@ -129,6 +133,8 @@ export class LocalBashExecutor extends BashExecutor {
       timeoutMs: spec.timeoutMs,
       maxOutputBytes: this.config.maxOutputBytes,
       signal: spec.signal,
+      stdin: spec.stdin,
+      env: spec.env,
     }, this.internals).done
     return { ...outcome, timeoutMs: spec.timeoutMs }
   }
@@ -145,6 +151,8 @@ export class LocalBashExecutor extends BashExecutor {
       timeoutMs: 0,
       maxOutputBytes: this.config.maxOutputBytes,
       signal: spec.signal,
+      stdin: spec.stdin,
+      env: spec.env,
     }, this.internals)
 
     const id = BashTaskId(`bash-${this.nextTaskId++}`)
diff --git a/packages/bash/bash-local/src/run.ts b/packages/bash/bash-local/src/run.ts
index 8a8d2065d2..023ea0e3d1 100644
--- a/packages/bash/bash-local/src/run.ts
+++ b/packages/bash/bash-local/src/run.ts
@@ -15,7 +15,8 @@
  * @module dsh-bash-local/run
  */
 
-import { spawn } from 'node:child_process'
+import { type ChildProcessByStdio, spawn } from 'node:child_process'
+import type { Readable, Writable } from 'node:stream'
 import { randomBytes } from 'node:crypto'
 import { closeSync, mkdtempSync, openSync, writeSync } from 'node:fs'
 import { tmpdir } from 'node:os'
@@ -42,13 +43,26 @@ export const ENV_OVERRIDES = {
  */
 export const SENSITIVE_ENV_PATTERN = /KEY|SECRET|TOKEN/i
 
-/** process.env minus credential-shaped vars, plus the model-friendly overrides. */
-export function childEnv(): NodeJS.ProcessEnv {
+/**
+ * `process.env` minus credential-shaped vars, plus the model-friendly
+ * overrides, plus any caller-supplied `extra` entries.
+ *
+ * Layering matters: the scrub drops `process.env` credentials, then
+ * `ENV_OVERRIDES` forces the model-friendly terminal vars, then `extra` is
+ * merged LAST so an explicit caller entry wins even when its name matches the
+ * scrub pattern (the scrub is the control that stops the HARNESS's ambient
+ * credentials leaking into a spawned command; a caller that explicitly sets a
+ * var named a value it already holds, not that ambient secret). `extra` is set
+ * by in-process plugins (the hooks bridges), not the model — `dsh-tool-bash`
+ * builds its request from named fields only and does not forward model input
+ * here (see its README, § "The tool builds its request from named args only").
+ */
+export function childEnv(extra?: Record<string, string>): NodeJS.ProcessEnv {
   const env: NodeJS.ProcessEnv = {}
   for (const [key, value] of Object.entries(process.env)) {
     if (!SENSITIVE_ENV_PATTERN.test(key)) env[key] = value
   }
-  return { ...env, ...ENV_OVERRIDES }
+  return { ...env, ...ENV_OVERRIDES, ...extra }
 }
 
 /** What to run and under which limits (resolved — no defaults in here). */
@@ -61,6 +75,19 @@ export interface SpawnSpec {
   maxOutputBytes: number
   /** Abort signal — kills the process group when fired. */
   signal?: AbortSignal | undefined
+  /**
+   * Bytes to write to the child's stdin, then close it. Absent (or empty)
+   * leaves stdin closed/empty. Set by in-process plugins (the hooks bridges);
+   * the model-facing `dsh-tool-bash` tool does not thread model input here.
+   */
+  stdin?: string | undefined
+  /**
+   * Extra environment entries, merged onto the scrubbed env AFTER the
+   * credential scrub and the model-friendly overrides (so an explicit entry
+   * wins). Set by in-process plugins; the model-facing tool does not forward
+   * model input here.
+   */
+  env?: Record<string, string> | undefined
 }
 
 /** Raw outcome of one closed process (before result shaping). */
@@ -272,12 +299,20 @@ export function runBash(spec: SpawnSpec, internals: RunInternals = {}): RunningB
     throw new Error(`aborted before spawn: ${String(spec.signal.reason ?? 'aborted')}`)
   }
 
-  const child = spawn('bash', ['-c', spec.command], {
-    cwd: spec.cwd,
-    env: childEnv(),
-    stdio: ['ignore', 'pipe', 'pipe'],
-    detached: true,
-  })
+  // stdin is a pipe ONLY when the caller supplied bytes; with none it is `ignore`
+  // (fd 0 → /dev/null) — the exact pre-seam default. This matters: a spawn pipe
+  // and /dev/null are NOT observationally identical (node's pipe is an AF_UNIX
+  // socket, so a command that probes stdin's type — `test -c /dev/stdin`, `stat
+  // /proc/self/fd/0` — sees a char device vs a socket), so the no-stdin path
+  // (every model-driven call) must keep /dev/null rather than regress to a socket.
+  // Two LITERAL `stdio` tuples (not one variable tuple): only a literal lets the
+  // typed `spawn` overload infer non-null stdout/stderr, which the
+  // `ChildProcessByStdio` annotation captures (stdin `Writable | null`; stdout/
+  // stderr the non-null `Readable` the collectors attach to without a cast).
+  const env = childEnv(spec.env)
+  const child: ChildProcessByStdio<Writable | null, Readable, Readable> = spec.stdin !== undefined
+    ? spawn('bash', ['-c', spec.command], { cwd: spec.cwd, env, stdio: ['pipe', 'pipe', 'pipe'], detached: true })
+    : spawn('bash', ['-c', spec.command], { cwd: spec.cwd, env, stdio: ['ignore', 'pipe', 'pipe'], detached: true })
 
   const stdout = new OutputCollector(spec.maxOutputBytes, 'stdout', spillDir)
   const stderr = new OutputCollector(spec.maxOutputBytes, 'stderr', spillDir)
@@ -312,6 +347,24 @@ export function runBash(spec: SpawnSpec, internals: RunInternals = {}): RunningB
   }
   spec.signal?.addEventListener('abort', onAbort, { once: true })
 
+  // Write stdin and close it, but ONLY when the caller supplied bytes — with no
+  // stdin, fd 0 is `ignore` (/dev/null) and `child.stdin` is null. The error
+  // handler must exist whenever we write: an unhandled 'error' on the stream
+  // would throw and crash the host. We swallow the error rather than reject
+  // `done`, and that is correct for ANY stdin-write error, not just the common
+  // one — the stdin write is BEST-EFFORT, while the command's authoritative
+  // outcome is its exit code + captured output, which the `close` handler reports
+  // regardless of whether the write landed. The expected case is EPIPE (the child
+  // exited without reading, so closing our end of a still-full pipe fails); a rare
+  // non-EPIPE pipe fault means the command ran with incomplete stdin, and it
+  // surfaces that itself through its own exit/output (e.g. a hook that gets
+  // truncated JSON errors out) — rejecting here would instead discard that real
+  // output and turn it into an opaque infrastructure error, which is worse.
+  if (child.stdin !== null) {
+    child.stdin.on('error', () => { /* stdin write is best-effort; outcome rides on exit/output. */ })
+    child.stdin.end(spec.stdin)
+  }
+
   const done = new Promise<SpawnOutcome>((resolve, reject) => {
     child.on('error', (error) => {
       // Spawn-level failure (ENOENT cwd, EACCES, …): no close event with
diff --git a/packages/bash/bash-local/tests/executor.spec.ts b/packages/bash/bash-local/tests/executor.spec.ts
index 2a27f29731..cf6d1c267e 100644
--- a/packages/bash/bash-local/tests/executor.spec.ts
+++ b/packages/bash/bash-local/tests/executor.spec.ts
@@ -106,6 +106,23 @@ describe('LocalBashExecutor.run', () => {
     const { bash } = await setup()
     await expect(bash.run(bash.resolve({ command: 'true', workdir: '/nonexistent-dsh' }))).rejects.toThrow(/ENOENT/)
   })
+
+  it('resolve() carries stdin/env onto the spec, and run() threads them to the command', async () => {
+    const { bash } = await setup()
+    const spec = bash.resolve({ command: 'cat; echo "[$DSH_SEAM_VAR]"', stdin: 'piped\n', env: { DSH_SEAM_VAR: 'env-ok' } })
+    // resolve() keeps the stdin/env fields verbatim (optional, no default).
+    expect(spec.stdin).toBe('piped\n')
+    expect(spec.env).toEqual({ DSH_SEAM_VAR: 'env-ok' })
+    const result = await bash.run(spec)
+    expect(result.stdout.text).toBe('piped\n[env-ok]\n')
+  })
+
+  it('resolve() omits stdin/env when the request supplies neither', async () => {
+    const { bash } = await setup()
+    const spec = bash.resolve({ command: 'true' })
+    expect('stdin' in spec).toBe(false)
+    expect('env' in spec).toBe(false)
+  })
 })
 
 describe('LocalBashExecutor background tasks', () => {
@@ -131,6 +148,19 @@ describe('LocalBashExecutor background tasks', () => {
     await Promise.all([first.done, second.done])
   })
 
+  it('threads stdin and extra env into a background task', async () => {
+    const { bash } = await setup()
+    const task = bash.start(bash.resolve({
+      command: 'cat; echo "[$DSH_BG_VAR]"',
+      stdin: 'bg-stdin\n',
+      env: { DSH_BG_VAR: 'bg-env' },
+    }))
+    const read = await readUntil(bash, task.id, '[bg-env]')
+    expect(read.delta).toContain('bg-stdin')
+    await task.done
+    expect(task.exitCode).toBe(0)
+  })
+
   it('readOutput returns increments without re-delivery', async () => {
     const { bash } = await setup()
     const task = bash.start(bash.resolve({ command: 'echo first; sleep 1; echo second' }))
diff --git a/packages/bash/bash-local/tests/run.spec.ts b/packages/bash/bash-local/tests/run.spec.ts
index b770c4a6c1..3a1ff7c2c5 100644
--- a/packages/bash/bash-local/tests/run.spec.ts
+++ b/packages/bash/bash-local/tests/run.spec.ts
@@ -158,6 +158,62 @@ describe('runBash', () => {
   })
 })
 
+describe('stdin and extra env (set by in-process plugins)', () => {
+  it('writes stdin to the command and closes it', async () => {
+    const result = await runBash(spec('cat', { stdin: 'hello from stdin\n' })).done
+    expect(result.exitCode).toBe(0)
+    expect(result.stdout.text).toBe('hello from stdin\n')
+  })
+
+  it('a command that reads stdin sees EOF when none is supplied', async () => {
+    // No stdin → fd 0 is /dev/null, so `cat` reads EOF and exits 0 with no
+    // output (it does NOT block).
+    const result = await runBash(spec('cat')).done
+    expect(result.exitCode).toBe(0)
+    expect(result.stdout.text).toBe('')
+  })
+
+  it('gives fd 0 the exact pre-seam type: /dev/null when no stdin, a pipe when supplied', async () => {
+    // The no-stdin path must stay observationally identical to the pre-seam
+    // `ignore` default: a command that probes stdin's file type sees a char
+    // device (/dev/null). Regressing to an always-open pipe would make fd 0 a
+    // socket (node's spawn pipe is an AF_UNIX socket, not a FIFO), flipping
+    // `test -c /dev/stdin` for every model-driven call. When bytes ARE supplied,
+    // fd 0 is that pipe (a socket), as it must be to carry them.
+    const none = await runBash(spec('test -c /dev/stdin && echo char || echo other')).done
+    expect(none.stdout.text).toBe('char\n')
+    const piped = await runBash(spec('test -S /dev/stdin && echo socket || echo other', { stdin: 'x' })).done
+    expect(piped.stdout.text).toBe('socket\n')
+  })
+
+  it('merges extra env entries onto the scrubbed environment', async () => {
+    const result = await runBash(spec('echo "$DSH_EXTRA_ONE/$DSH_EXTRA_TWO"', {
+      env: { DSH_EXTRA_ONE: 'alpha', DSH_EXTRA_TWO: 'beta' },
+    })).done
+    expect(result.stdout.text).toBe('alpha/beta\n')
+  })
+
+  it('an explicit extra env entry overrides the model-friendly override and the scrub', async () => {
+    // TERM is a model-friendly OVERRIDE (dumb); an explicit extra entry wins.
+    // DSH_OVERRIDE_KEY matches the credential scrub pattern, yet an explicit
+    // entry is still honored — the scrub only drops AMBIENT process.env creds.
+    const result = await runBash(spec('echo "$TERM/$DSH_OVERRIDE_KEY"', {
+      env: { TERM: 'xterm-256color', DSH_OVERRIDE_KEY: 'explicit-wins' },
+    })).done
+    expect(result.stdout.text).toBe('xterm-256color/explicit-wins\n')
+  })
+
+  it('does not crash or reject when the child ignores a large stdin (EPIPE)', async () => {
+    // The child exits immediately without reading; closing our end of a stdin
+    // pipe still holding ~1MiB triggers EPIPE on the write. The handler must
+    // swallow it: `done` resolves normally with the child's real exit.
+    const big = 'x'.repeat(1024 * 1024)
+    const result = await runBash(spec('exit 7', { stdin: big })).done
+    expect(result.exitCode).toBe(7)
+    expect(result.aborted).toBe(false)
+  })
+})
+
 describe('output truncation and spill', () => {
   it('keeps the tail and spills the full stream to disk', async () => {
     // 200 numbered lines of ~10 bytes; cap at 500 bytes keeps a late tail.
diff --git a/packages/bash/bash/README.md b/packages/bash/bash/README.md
index 6123565e7a..39318ae371 100644
--- a/packages/bash/bash/README.md
+++ b/packages/bash/bash/README.md
@@ -28,4 +28,6 @@ Implementations subclass `BashExecutor`, implement the abstract methods, and cal
 
 ## Vocabulary
 
-`BashExecRequest` (command, workdir?, timeoutMs?, signal?, owner?) resolves to `BashExecSpec` (command, workdir, timeoutMs, signal?, owner) before execution; `owner` is optional on the request and **required-but-nullable** (`OwnerToken | undefined`) on the resolved spec, so a forgotten owner is a visible `undefined` rather than a silently-absent property. The task id (`BashTaskId`) and the `owner` token (`OwnerToken`) are [branded](../../util/brand) — `OwnerToken` is a DISTINCT brand from `SessionId` (the seam never imports `dsh-session`; the `dsh-tool-bash` consumer is the single boundary that casts its `SessionId` into one). `run()` returns `BashRunResult` (exitCode, signal, timedOut, aborted, timeoutMs, stdout/stderr as `CollectedOutput`) and `start()`/`readOutput()` use `BashTask`/`BashTaskRead` for the background side. See `src/types.ts` for the full contracts.
+`BashExecRequest` (command, workdir?, timeoutMs?, signal?, stdin?, env?, owner?) resolves to `BashExecSpec` (command, workdir, timeoutMs, signal?, stdin?, env?, owner) before execution; `owner` is optional on the request and **required-but-nullable** (`OwnerToken | undefined`) on the resolved spec, so a forgotten owner is a visible `undefined` rather than a silently-absent property. The task id (`BashTaskId`) and the `owner` token (`OwnerToken`) are [branded](../../util/brand) — `OwnerToken` is a DISTINCT brand from `SessionId` (the seam never imports `dsh-session`; the `dsh-tool-bash` consumer is the single boundary that casts its `SessionId` into one). `run()` returns `BashRunResult` (exitCode, signal, timedOut, aborted, timeoutMs, stdout/stderr as `CollectedOutput`) and `start()`/`readOutput()` use `BashTask`/`BashTaskRead` for the background side. See `src/types.ts` for the full contracts.
+
+`stdin` and `env` are set by in-process plugins (the hooks bridges, native plugins) to feed a hook command its JSON payload on stdin and its `CLAUDE_PROJECT_DIR`/`CLAUDE_PLUGIN_ROOT` env. The model-facing `dsh-tool-bash` tool does not expose them as parameters — a model already has equivalent power through shell syntax (`FOO=bar cmd`, a heredoc), so they would be redundant tool params. This is not a security boundary: the implementation's credential scrub (not these fields) is what keeps the harness's ambient secrets out of a spawned command. They are plain optionals on the resolved spec (unlike `owner`'s required-but-nullable): a missing one means "none", the safe default. See [the bash-stdin-env RFC](../../../docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
diff --git a/packages/bash/bash/src/types.ts b/packages/bash/bash/src/types.ts
index d9ab9f9b4d..9acd5c7cb7 100644
--- a/packages/bash/bash/src/types.ts
+++ b/packages/bash/bash/src/types.ts
@@ -45,6 +45,24 @@ export interface BashExecRequest {
   timeoutMs?: number | undefined
   /** Abort signal — implementations kill the command when it fires. */
   signal?: AbortSignal | undefined
+  /**
+   * Bytes to write to the command's stdin, then close it. Absent leaves stdin
+   * closed/empty (the default for model-driven tool calls). Set by in-process
+   * plugins (e.g. the hooks bridges, which write a hook command's JSON payload
+   * to its stdin); the model-facing bash tool does not expose it as a parameter
+   * (a model that needs stdin uses shell syntax like a heredoc or a pipe).
+   */
+  stdin?: string | undefined
+  /**
+   * Extra environment entries for the command, merged AFTER the
+   * implementation's credential scrub (so an explicit entry here is honored even
+   * when its name matches the scrub pattern — the caller named a value it holds,
+   * not the harness's ambient secret). Set by in-process plugins (the hooks
+   * bridges set `CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, …); the model-facing
+   * bash tool does not expose it as a parameter (a model that needs an env var
+   * uses shell syntax like `FOO=bar cmd`).
+   */
+  env?: Record<string, string> | undefined
   /**
    * Opaque OWNER token for a background task — the consumer's isolation key
    * (the tool layer passes the owning agent's `session.header.id`). The
@@ -70,6 +88,22 @@ export interface BashExecSpec {
   timeoutMs: number
   /** Abort signal — implementations kill the command when it fires. */
   signal?: AbortSignal | undefined
+  /**
+   * Bytes to write to the command's stdin (then close it), carried through
+   * verbatim from {@link BashExecRequest.stdin}. OPTIONAL on the resolved spec
+   * (unlike `owner`): it has no config default, so a missing one means "no
+   * stdin" — the safe, ordinary case — not a silent footgun, so it stays a
+   * plain optional rather than required-but-nullable (see the request field).
+   */
+  stdin?: string | undefined
+  /**
+   * Extra environment entries, carried through verbatim from
+   * {@link BashExecRequest.env} and merged by the implementation AFTER its
+   * credential scrub (an explicit entry wins even when its name matches the
+   * scrub pattern). OPTIONAL on the spec for the same reason as `stdin` — no
+   * config default, absent means "no extra env".
+   */
+  env?: Record<string, string> | undefined
   /**
    * Opaque owner token, REQUIRED-but-nullable (mirrors `workdir`/`timeoutMs`
    * being required on the resolved spec): {@link BashExecutor.resolve} carries
diff --git a/packages/bash/tool-bash/README.md b/packages/bash/tool-bash/README.md
index 29cec70970..3951e2705b 100644
--- a/packages/bash/tool-bash/README.md
+++ b/packages/bash/tool-bash/README.md
@@ -40,6 +40,10 @@ These tools own how their calls render in a UI (an editor's tool-call card) via
 
 When a background task finishes, a short notice is injected into the owning agent's session (`agent.inject()`, source `{kind: 'plugin', plugin: 'tool-bash'}`). The owning agent is found by its session token: the listener reads `ctx.bash.ownerOf(task.id)` and scans `ctx.get('agents')?.list()` for an agent whose `session.header.id` matches (read via `ctx.get` — `onTaskDone` runs on the bash fiber, a foreign fiber, so the `ctx.agents` proxy would throw). If no live agent carries that token — e.g. the owning session disconnected and its agent was disposed while the task ran on — the notice is dropped cleanly. Injection is **durable context for the next model request, not a wake-up** — an idle agent stays idle until something sends a message. That's why the tool descriptions tell the model to poll with `bash_output`.
 
+## The tool builds its request from named args only
+
+The `BashExecRequest` seam carries optional `stdin` and `env`, used by the hooks bridges to feed a hook command its JSON payload and `CLAUDE_*` env. This tool does **not** expose them as parameters: its request is built from `command`/`workdir`/`timeoutMs`/`signal`/`owner` only, so a model that includes `env` or `stdin` keys in its tool arguments has them ignored. This is not a trust boundary — a model already has equivalent power through shell syntax (`FOO=bar cmd`, a heredoc), and the real defense against leaking the harness's ambient secrets is `dsh-bash-local`'s credential scrub, which works regardless. A regression guard drives the real tool with those extra args and asserts the resulting request carries neither field — its job is to catch a future refactor that blindly spreads `...args` into the request (which would silently forward model input into the post-scrub `env` merge), not to defend a wall. See [the bash-stdin-env RFC](../../../docs/rfc/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md).
+
 ## Permissions
 
 `TODO(permissions)`: commands run with the executor's full authority. The permission/sandbox seam is the `tools/execute` waterfall (veto or ask) plus sandboxing `BashExecutor` implementations — see docs/architecture.md. `@cordisjs/plugin-capability` (a named-permission service with a session `test()`) is a candidate building block for that work.
diff --git a/packages/bash/tool-bash/tests/tools.spec.ts b/packages/bash/tool-bash/tests/tools.spec.ts
index 368ed4fdd7..82b69fb133 100644
--- a/packages/bash/tool-bash/tests/tools.spec.ts
+++ b/packages/bash/tool-bash/tests/tools.spec.ts
@@ -857,3 +857,105 @@ describe('tool-owned UI presentation (presentCall / presentResult)', () => {
     expect(ctx.tools.get('bash')?.presentCall?.({ command: 'ls' })).toBeUndefined()
   })
 })
+
+describe('the model-facing bash tool builds its request from named args only (no {...args} forward)', () => {
+  /**
+   * Records every {@link BashExecRequest} the consumer hands to `resolve()`, so a
+   * test can assert what the model-facing tool DID and DID NOT forward. The `bash`
+   * tool does not expose `stdin`/`env` as parameters (bash syntax already gives a
+   * model that power), so it must build its request from named args only and
+   * never spread unknown tool-call keys into it. This guard's job is to catch a
+   * future refactor that blindly forwards `...args` — which would silently thread
+   * model input into the post-scrub `env` merge — NOT to defend a trust boundary
+   * (the credential scrub in dsh-bash-local is the security control; see the
+   * bash-stdin-env RFC). Foreground `run()` returns a canned result; `start()` is
+   * unused here.
+   */
+  class RecordingBashExecutor extends BashExecutor {
+    readonly requests: BashExecRequest[] = []
+    resolve(request: BashExecRequest): BashExecSpec {
+      this.requests.push(request)
+      return {
+        command: request.command,
+        workdir: request.workdir ?? process.cwd(),
+        timeoutMs: request.timeoutMs ?? 0,
+        ...request.signal ? { signal: request.signal } : {},
+        ...request.stdin !== undefined ? { stdin: request.stdin } : {},
+        ...request.env !== undefined ? { env: request.env } : {},
+        owner: request.owner,
+      }
+    }
+    run(): Promise<BashRunResult> {
+      return Promise.resolve({
+        exitCode: 0, signal: null, timedOut: false, aborted: false, timeoutMs: 0,
+        stdout: { text: 'ok', truncated: false }, stderr: { text: '', truncated: false },
+      })
+    }
+    start(): BashTask { throw new Error('unused') }
+    get(): BashTask | undefined { return undefined }
+    ownerOf(): OwnerToken | undefined { return undefined }
+    list(): BashTask[] { return [] }
+    readOutput(): BashTaskRead { throw new Error('unused') }
+    kill(): boolean { return false }
+  }
+
+  async function setupRecording() {
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(AgentRegistry)
+    await ctx.plugin(RecordingBashExecutor)
+    await ctx.plugin(ToolBash)
+    return { ctx, bash: ctx.bash as RecordingBashExecutor }
+  }
+
+  it('does not forward env/stdin even when the model includes them as extra arguments', async () => {
+    const { ctx, bash } = await setupRecording()
+    // Extra args: the model includes `env` and `stdin` keys hoping they reach the
+    // executor. The bash tool's schema ignores unknown keys, and execute() builds
+    // the request from only command/workdir/timeoutMs/signal — so the recorded
+    // request carries NEITHER. (Not a security wall — the model could set an env
+    // var or feed stdin via shell syntax anyway; this just keeps the request
+    // shape honest so a future `...args` spread can't silently forward input.)
+    await ctx.tools.execute({
+      callId: CallId('no-forward-1'),
+      name: 'bash',
+      arguments: {
+        command: 'echo hi',
+        description: 'echo',
+        env: { SNEAKY_API_KEY: 'leak' },
+        stdin: 'malicious payload',
+      },
+    })
+    expect(bash.requests).toHaveLength(1)
+    const request = bash.requests[0]!
+    expect(request.command).toBe('echo hi')
+    expect('env' in request).toBe(false)
+    expect('stdin' in request).toBe(false)
+  })
+
+  it('a background bash call likewise carries no env/stdin', async () => {
+    const { ctx, bash } = await setupRecording()
+    // start() throws in this recorder, but resolve() runs first and records the
+    // request — which is all this no-forward assertion needs.
+    await ctx.tools.execute({
+      callId: CallId('no-forward-2'),
+      name: 'bash',
+      arguments: {
+        command: 'sleep 1',
+        description: 'sleep',
+        run_in_background: true,
+        env: { TOKEN: 'leak' },
+        stdin: 'x',
+      },
+    })
+    expect(bash.requests).toHaveLength(1)
+    const request = bash.requests[0]!
+    expect('env' in request).toBe(false)
+    expect('stdin' in request).toBe(false)
+    // The owner token IS set on a background call (the isolation fence) — proving
+    // the recorder sees the real request the consumer built, so the absent
+    // env/stdin above is a real negative, not a recorder that drops everything.
+    expect('owner' in request).toBe(true)
+  })
+})