From 2f98a20b5ff967c42fc2246e12b560431fa28a99 Mon Sep 17 00:00:00 2001
From: Kyle Mistele <kyle@humanlayer.dev>
Date: Wed, 26 Aug 2026 20:43:59 -0700
Subject: [PATCH] feat(fold-agent): pass host environment to bash

HumanLayer-Session: https://app.dev.codelayer.gg/sessions/01a04147-8de0-7e74-9371-1012b821fab4
---
 packages/fold-agent/src/Tools/BashTool.ts     |  6 +++-
 packages/fold-agent/src/Tools/CodingTools.ts  |  6 ++--
 .../fold-agent/test/Tools/BashTool.vi.test.ts | 36 ++++++++++++++++++-
 3 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/packages/fold-agent/src/Tools/BashTool.ts b/packages/fold-agent/src/Tools/BashTool.ts
index ea5b732..bc6be24 100644
--- a/packages/fold-agent/src/Tools/BashTool.ts
+++ b/packages/fold-agent/src/Tools/BashTool.ts
@@ -85,6 +85,8 @@ export type BashToolOptions = FsToolOptions & {
 	readonly spillDir?: string
 	/** Deterministic per-session output store. When absent, bash uses the legacy temp spill file. */
 	readonly outputStore?: OutputStoreService
+	/** Environment entries inherited by every Bash subprocess created by this tool. */
+	readonly processEnvironment?: Readonly<Record<string, string>>
 }
 
 type AccumulatorState = {
@@ -328,12 +330,14 @@ export const bashTool = (options?: BashToolOptions): FoldTool =>
 					})
 
 				const run = Effect.gen(function* () {
+					const inheritedPath = options?.processEnvironment?.PATH ?? process.env.PATH ?? ''
 					const handle = yield* spawner
 						.spawn(
 							ChildProcess.make('bash', ['-c', params.command], {
 								cwd,
 								env: {
-									PATH: `${pathService.join(homedir(), '.fold', 'bin')}:${process.env.PATH ?? ''}`,
+									...options?.processEnvironment,
+									PATH: `${pathService.join(homedir(), '.fold', 'bin')}:${inheritedPath}`,
 								},
 								extendEnv: true,
 							}),
diff --git a/packages/fold-agent/src/Tools/CodingTools.ts b/packages/fold-agent/src/Tools/CodingTools.ts
index c83ce88..8edbba1 100644
--- a/packages/fold-agent/src/Tools/CodingTools.ts
+++ b/packages/fold-agent/src/Tools/CodingTools.ts
@@ -14,8 +14,10 @@ import { readTool } from './ReadTool'
 import { webTools, type WebToolsOptions } from './WebTools'
 import { writeTool } from './WriteTool'
 
-/** Options for {@link codingTools}: the shared filesystem seam plus bash output-spill configuration. */
-export type CodingToolsOptions = FsToolOptions & Pick<BashToolOptions, 'spillDir' | 'outputStore'> & WebToolsOptions
+/** Options for {@link codingTools}: the shared filesystem seam plus Bash process configuration. */
+export type CodingToolsOptions = FsToolOptions &
+	Pick<BashToolOptions, 'spillDir' | 'outputStore' | 'processEnvironment'> &
+	WebToolsOptions
 
 /**
  * The standard coding toolset: read, write, edit, apply_patch, bash, and web tools. The model-family policy decides
diff --git a/packages/fold-agent/test/Tools/BashTool.vi.test.ts b/packages/fold-agent/test/Tools/BashTool.vi.test.ts
index fc84fcb..b15ad2d 100644
--- a/packages/fold-agent/test/Tools/BashTool.vi.test.ts
+++ b/packages/fold-agent/test/Tools/BashTool.vi.test.ts
@@ -11,7 +11,7 @@ import { expect, it } from '@effect/vitest'
 import { SessionId, ToolCallId } from '@humanlayer/fold-core'
 import { Duration, Effect, Fiber } from 'effect'
 
-import { bashTool, decodeBashOutputDelta, makeOutputStore, toolOutputPathFor } from '../../src/index'
+import { bashTool, codingTools, decodeBashOutputDelta, makeOutputStore, toolOutputPathFor } from '../../src/index'
 import { handlerOf, makeAmbientServices, messageOf, outputOf, runHandler, tempDir } from '../TestHelpers'
 
 it.live('captures stdout and reports success on exit 0', () =>
@@ -23,6 +23,40 @@ it.live('captures stdout and reports success on exit 0', () =>
 	}),
 )
 
+it.live('passes host-provided session environment to Bash subprocesses', () =>
+	Effect.gen(function* () {
+		const dir = yield* tempDir
+		const result = yield* runHandler(
+			handlerOf(
+				bashTool({
+					cwd: dir,
+					processEnvironment: {
+						HUMANLAYER_SESSION_ID: 'session-from-host',
+						HUMANLAYER_SESSION_EXPIRES: '4102444800000',
+					},
+				}),
+			)({ command: 'printf "%s:%s" "$HUMANLAYER_SESSION_ID" "$HUMANLAYER_SESSION_EXPIRES"' }),
+		)
+
+		expect(outputOf(result)).toBe('session-from-host:4102444800000')
+	}),
+)
+
+it.live('forwards host-provided session environment through codingTools', () =>
+	Effect.gen(function* () {
+		const dir = yield* tempDir
+		const bash = codingTools({
+			cwd: dir,
+			processEnvironment: { HUMANLAYER_SESSION_ID: 'coding-tools-session' },
+		}).find((tool) => tool.name === 'bash')
+		if (bash === undefined) throw new Error('expected codingTools to include Bash')
+
+		const result = yield* runHandler(handlerOf(bash)({ command: 'printf "%s" "$HUMANLAYER_SESSION_ID"' }))
+
+		expect(outputOf(result)).toBe('coding-tools-session')
+	}),
+)
+
 it.live('interleaves stderr into the same output buffer', () =>
 	Effect.gen(function* () {
 		const dir = yield* tempDir