diff --git a/docs/compatibility.md b/docs/compatibility.md
index 67140e6..6ffab0e 100644
--- a/docs/compatibility.md
+++ b/docs/compatibility.md
@@ -76,6 +76,7 @@ Last verified: **2026-10-14** (dsh-context `0.70.0`, dsh `0.2.0-rc.2` npm instal
 5. **Re-prove everything at the boundary** — collections re-proven, scalars zeroed, whole-value absence stays `null` (the loading screen); structural narrowing over blind casts; skip elements that fail the shape instead of throwing. (`src/client/timelineSource.ts`)
 6. **Isolate per-item work over hostile objects**; every async read resolves to data or a retryable failure note — never an eternal spinner. (`src/client/timelineSource.ts`)
 7. **A pushed revision decrease resets the detail ledger** — stale reads never merge into the new head. (`src/client/timelineSource.ts`)
+8. **Fetch routes ride browser-relative spellings** (issue #159) — the client never issues a root-absolute `/api/...` URL: fetch resolves the relative form against the page's document base, so a deployment behind a path-prefixed reverse proxy (page at `/app/dsh/`) keeps its prefix, where a root-absolute spelling 404s at the gateway. (`src/client/apiRoutes.ts`)
 
 - **Limitation — complete prompt sections:** a deployment registering a `complete` system-prompt section keeps ONLY that section (registry design); `promptPrefix`/`promptSuffix` are dropped there. (dsh: `packages/core/system-prompt`)
 
diff --git a/src/client/apiRoutes.ts b/src/client/apiRoutes.ts
new file mode 100644
index 0000000..7951b5e
--- /dev/null
+++ b/src/client/apiRoutes.ts
@@ -0,0 +1,17 @@
+/** The plugin's fetch routes, in their browser-relative spellings — the host halves register the
+ * absolute `/api/...` paths under the harness's authenticated fence (host/detail.ts and siblings).
+ * Re-declared here because the client bundle inlines every import and must never reach a host module.
+ * Relative on purpose (docs/compatibility.md §5.8, issue #159): a root-absolute spelling would drop
+ * a reverse proxy's path prefix at the gateway. */
+
+export const DETAIL_ROUTE = 'api/dsh-context/detail'
+
+export const BALANCE_ROUTE = 'api/dsh-context/balance'
+
+export const FLEET_ROUTE = 'api/dsh-context/fleet'
+
+export const SKILLS_ROUTE = 'api/dsh-context/skills'
+
+export const BACKFILL_ROUTE = 'api/dsh-context/backfill'
+
+export const ATTACHMENT_ROUTE = 'api/dsh-context/attachment'
diff --git a/src/client/attachmentSource.ts b/src/client/attachmentSource.ts
index 5bbaa08..56e1993 100644
--- a/src/client/attachmentSource.ts
+++ b/src/client/attachmentSource.ts
@@ -8,13 +8,10 @@
 
 import { previewAddressOf } from './fileActivity'
 import type { AttachmentRef } from '../shared/attachment'
+import { ATTACHMENT_ROUTE } from './apiRoutes'
 import { asRecord, openResourceVia } from './services'
 import type { AttachmentLocator, AttachmentOpener, ClientCtx } from './services'
 
-// The route of host/attachment.ts, re-declared here: the client bundle inlines every import and the
-// host module must never reach it (the detail route's own arrangement in timelineSource.ts).
-const ATTACHMENT_ROUTE = '/api/dsh-context/attachment'
-
 /** Cache ceiling: cards are clicked one at a time, so a small FIFO holds a session's working set. */
 const CACHE_MAX = 32
 
diff --git a/src/client/balance.ts b/src/client/balance.ts
index 818710e..8c2094b 100644
--- a/src/client/balance.ts
+++ b/src/client/balance.ts
@@ -4,12 +4,9 @@
  * spinner or an error where a pill should be. */
 
 import type { PlatformBalance, PlatformBalanceEntry } from '../shared/types'
+import { BALANCE_ROUTE } from './apiRoutes'
 import { asRecord } from './services'
 
-// The balance route of host/balance.ts, re-declared because the client bundle inlines every import;
-// same-origin POST under the harness's authenticated `/api` fence.
-const BALANCE_ROUTE = '/api/dsh-context/balance'
-
 const STORAGE_KEY = 'dsh-context:platform-balance'
 
 export interface StorageFace {
diff --git a/src/client/fleetDetail.ts b/src/client/fleetDetail.ts
index ce88f08..9f1b07c 100644
--- a/src/client/fleetDetail.ts
+++ b/src/client/fleetDetail.ts
@@ -9,12 +9,9 @@
  */
 
 import type { FleetDetail, FleetDescriptor, FleetMemberInfo, FleetMessage } from '../shared/types'
+import { FLEET_ROUTE } from './apiRoutes'
 import { asRecord, numOf } from './services'
 
-// The route of host/fleet.ts, re-declared here: the client bundle inlines every import and the
-// host module must never reach it.
-const FLEET_ROUTE = '/api/dsh-context/fleet'
-
 function strings(value: unknown): string | undefined {
   return typeof value === 'string' && value !== '' ? value : undefined
 }
diff --git a/src/client/overview.ts b/src/client/overview.ts
index 2deb994..cfc54b8 100644
--- a/src/client/overview.ts
+++ b/src/client/overview.ts
@@ -11,6 +11,7 @@
 
 import { workspaceTitleOf } from '@deepseek-ai/dsh-util-workspace-path'
 import { dayKeyOf, endOfDayKey, startOfDayKey } from '../shared/days'
+import { BACKFILL_ROUTE } from './apiRoutes'
 import { billedParts } from './categories'
 import { cacheHitPercent } from './format'
 import { estimateSessionCost, mergeCostUsage } from './cost'
@@ -713,10 +714,6 @@ export function refreshSessions(ctx: ClientCtx): void {
   } catch { /* hostile service — no refresh */ }
 }
 
-// The plugin's warm-up trigger route (host/backfill.ts), re-declared here: the
-// client bundle inlines every import and the host module must never reach it.
-const BACKFILL_ROUTE = '/api/dsh-context/backfill'
-
 /** Summon the host's projection warm-up (host/backfill.ts): this page is
  * the rows' only reader, so the host defers the corpus-wide cold reads until
  * this surface first opens (one pass per host process). */
diff --git a/src/client/skills.ts b/src/client/skills.ts
index fc0bd30..37a5eca 100644
--- a/src/client/skills.ts
+++ b/src/client/skills.ts
@@ -3,12 +3,9 @@
  * current session; a failed read renders the tallies unenriched. */
 
 import type { SkillInfo } from '../shared/types'
+import { SKILLS_ROUTE } from './apiRoutes'
 import { asRecord } from './services'
 
-// The skills route of host/skills.ts, re-declared here: the client bundle
-// inlines every import and the host module must never reach it.
-const SKILLS_ROUTE = '/api/dsh-context/skills'
-
 /** Narrow the route's payload: the name is the join key and must prove itself; path and source ride only when proved. */
 export function skillInfoListOf(value: unknown): SkillInfo[] | null {
   const list = asRecord(value)?.skills
diff --git a/src/client/timelineSource.ts b/src/client/timelineSource.ts
index 563dacd..23e9518 100644
--- a/src/client/timelineSource.ts
+++ b/src/client/timelineSource.ts
@@ -16,13 +16,10 @@
 
 import { useEffect, useMemo, useSyncExternalStore } from 'react'
 import type { ContextTimeline, ContextTimelineDetail } from '../shared/types'
+import { DETAIL_ROUTE } from './apiRoutes'
 import type { SessionStandardProps } from './services'
 import { asRecord, collectionsOf, projectionOf, timelineOf } from './services'
 
-// The detail route of host/detail.ts, re-declared here: the client bundle
-// inlines every import and the host module must never reach it.
-const DETAIL_ROUTE = '/api/dsh-context/detail'
-
 /** Narrow the detail endpoint's payload; a missing or NaN revision rejects the
  * whole payload so the caller shows its retryable note, never half-merged data. */
 export function detailOf(value: unknown): ContextTimelineDetail | null {
diff --git a/tests/client/apiRoutes.spec.ts b/tests/client/apiRoutes.spec.ts
new file mode 100644
index 0000000..0861b25
--- /dev/null
+++ b/tests/client/apiRoutes.spec.ts
@@ -0,0 +1,18 @@
+import assert from 'node:assert/strict'
+import { describe, test } from 'vitest'
+import {
+  ATTACHMENT_ROUTE,
+  BACKFILL_ROUTE,
+  BALANCE_ROUTE,
+  DETAIL_ROUTE,
+  FLEET_ROUTE,
+  SKILLS_ROUTE,
+} from '../../src/client/apiRoutes'
+
+describe('apiRoutes', () => {
+  test('every fetch route stays browser-relative under the plugin namespace', () => {
+    for (const route of [ATTACHMENT_ROUTE, BACKFILL_ROUTE, BALANCE_ROUTE, DETAIL_ROUTE, FLEET_ROUTE, SKILLS_ROUTE]) {
+      assert.match(route, /^api\/dsh-context\/\w+$/, route)
+    }
+  })
+})
diff --git a/tests/client/attachmentSource.spec.ts b/tests/client/attachmentSource.spec.ts
index 9b894c7..aa598e6 100644
--- a/tests/client/attachmentSource.spec.ts
+++ b/tests/client/attachmentSource.spec.ts
@@ -64,7 +64,7 @@ describe('makeAttachmentLocator', () => {
     assert.equal(await locate(FILE), ALIAS)
     assert.equal(await locate(FILE), ALIAS)
     assert.equal(calls.length, 1, 'the second read is served from the cache')
-    assert.equal(calls[0].url, '/api/dsh-context/attachment')
+    assert.equal(calls[0].url, 'api/dsh-context/attachment')
     assert.deepEqual(calls[0].body, { sessionId: 's1', attachmentId: 'sha256:f1' })
   })
 
diff --git a/tests/client/components/agentGraph.spec.ts b/tests/client/components/agentGraph.spec.ts
index 302d8dc..9c324d7 100644
--- a/tests/client/components/agentGraph.spec.ts
+++ b/tests/client/components/agentGraph.spec.ts
@@ -664,7 +664,7 @@ describe('AgentGraph — cold-relative composition fetch', () => {
     const m = await mount(h(View, { sessionId: 'root', self: selfStats() }))
 
     // The cold relative fetched at mount; until the read lands it wears the pressure-only fill.
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'])
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'])
     assert.equal(query(m.container, '[data-agent="done"]').querySelectorAll('.lc-agent-bar-seg').length, 1)
 
     // A snapshot tick while the read is in flight re-attaches the SAME
@@ -688,14 +688,14 @@ describe('AgentGraph — cold-relative composition fetch', () => {
       face.setState(family())
     })
     await flush()
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'])
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'])
 
     // A remount (tab switch) resets the instance state but replays the
     // factory-cached read: the bar recomposes with no new request.
     await m.unmount()
     const remounted = await mount(h(View, { sessionId: 'root', self: selfStats() }))
     await flush()
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'], 'the cache never re-fetches')
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'], 'the cache never re-fetches')
     const replayed = query(remounted.container, '[data-agent="done"]')
     assert.equal(replayed.querySelectorAll('.lc-agent-bar-seg').length, 6, 'the cached head replays into the fresh instance')
     await remounted.unmount()
@@ -706,14 +706,14 @@ describe('AgentGraph — cold-relative composition fetch', () => {
     const { View, face } = makeFetchingView()
     const m = await mount(h(View, { sessionId: 'root', self: selfStats() }))
     await flush()
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'])
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'])
     assert.equal(query(m.container, '[data-agent="done"]').querySelectorAll('.lc-agent-bar-seg').length, 1)
     // A later snapshot tick (fresh forest, still pressure-only) re-fetches nothing.
     await act(async () => {
       face.setState(family())
     })
     await flush()
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'], 'the sticky failure never re-fetches')
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'], 'the sticky failure never re-fetches')
     await m.unmount()
   })
 
@@ -723,7 +723,7 @@ describe('AgentGraph — cold-relative composition fetch', () => {
       const { View } = makeFetchingView()
       const m = await mount(h(View, { sessionId: 'root', self: selfStats() }))
       await flush()
-      assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:done'])
+      assert.deepEqual(rpc.calls, ['api/dsh-context/detail:done'])
       assert.equal(query(m.container, '[data-agent="done"]').querySelectorAll('.lc-agent-bar-seg').length, 1)
       assert.ok(text(query(m.container, '[data-agent="done"]')).includes('95%'))
       await m.unmount()
@@ -762,7 +762,7 @@ describe('AgentGraph — cold-relative composition fetch', () => {
     const View = makeAgentGraph(asClientCtx(ctx), kit)
     const m = await mount(h(View, { sessionId: 'root', self: selfStats() }))
     assert.equal(query(m.container, '[data-agent="cold"]').querySelectorAll('.lc-agent-bar-seg').length, 0)
-    assert.deepEqual(rpc.calls, ['/api/dsh-context/detail:cold'])
+    assert.deepEqual(rpc.calls, ['api/dsh-context/detail:cold'])
 
     await act(async () => {
       rpc.release({ ok: true, status: 200, json: async () => ({ ok: true, value: detailValue(composedHead()) }) })
diff --git a/tests/client/components/overviewPanel.spec.ts b/tests/client/components/overviewPanel.spec.ts
index 7f7ae49..36225f4 100644
--- a/tests/client/components/overviewPanel.spec.ts
+++ b/tests/client/components/overviewPanel.spec.ts
@@ -135,7 +135,7 @@ describe('OverviewPanel', () => {
     const ctx = makeCtx({ refresh: () => { pulls++; return Promise.resolve() } })
     const { m } = await openPanel(ctx)
     assert.equal(pulls, 1, 'the baseline re-pull fires on mount')
-    assert.deepEqual(backfillPosts, ['/api/dsh-context/backfill'], 'the warm-up trigger POST fires on mount')
+    assert.deepEqual(backfillPosts, ['api/dsh-context/backfill'], 'the warm-up trigger POST fires on mount')
     assert.ok(text(m.container).includes('Context Insights'))
     // The page chrome: the section's one scroll region carries the centered
     // content column — the page heading, then the 1:1 first row (the KPI
diff --git a/tests/client/overview.sessions.spec.ts b/tests/client/overview.sessions.spec.ts
index d1f5da2..838bd96 100644
--- a/tests/client/overview.sessions.spec.ts
+++ b/tests/client/overview.sessions.spec.ts
@@ -240,7 +240,7 @@ describe('requestActivityBackfill', () => {
       return { ok: true }
     })
     requestActivityBackfill()
-    assert.deepEqual(calls, [['/api/dsh-context/backfill', { method: 'POST' }]])
+    assert.deepEqual(calls, [['api/dsh-context/backfill', { method: 'POST' }]])
     vi.stubGlobal('fetch', async () => Promise.reject(new Error('route absent')))
     requestActivityBackfill()
     vi.stubGlobal('fetch', () => { throw new Error('hostile transport') })
diff --git a/tests/client/skills.spec.ts b/tests/client/skills.spec.ts
index 4122073..def74fe 100644
--- a/tests/client/skills.spec.ts
+++ b/tests/client/skills.spec.ts
@@ -66,7 +66,7 @@ describe('readSkillCatalog', () => {
       },
     })
     const catalog = await readSkillCatalog('/repo/alpha', 's1')
-    assert.deepEqual(urls, ['/api/dsh-context/skills'])
+    assert.deepEqual(urls, ['api/dsh-context/skills'])
     assert.deepEqual(bodies, [{ cwd: '/repo/alpha', sessionId: 's1' }])
     assert.equal(catalog?.size, 2)
     assert.deepEqual(catalog?.get('tdd'), { name: 'tdd', description: 'Test-driven', path: '/p/tdd/SKILL.md', source: 'user-agents' })
diff --git a/tests/client/timelineSource.spec.ts b/tests/client/timelineSource.spec.ts
index 3d0eb23..b7aedfa 100644
--- a/tests/client/timelineSource.spec.ts
+++ b/tests/client/timelineSource.spec.ts
@@ -156,7 +156,7 @@ describe('makeDetailFetcher', () => {
     })
     const d = await makeDetailFetcher('s1')!()
     assert.equal(d?.rev, 4)
-    assert.equal(seen.url, '/api/dsh-context/detail')
+    assert.equal(seen.url, 'api/dsh-context/detail')
     assert.deepEqual(seen.body, { sessionId: 's1' })
   })
 })
diff --git a/tests/host/apiRoutes.spec.ts b/tests/host/apiRoutes.spec.ts
new file mode 100644
index 0000000..08903c9
--- /dev/null
+++ b/tests/host/apiRoutes.spec.ts
@@ -0,0 +1,31 @@
+import assert from 'node:assert/strict'
+import { describe, test } from 'vitest'
+import { BALANCE_ROUTE as HOST_BALANCE_ROUTE } from '../../src/host/balance'
+import { DETAIL_ROUTE as HOST_DETAIL_ROUTE } from '../../src/host/detail'
+import { ATTACHMENT_ROUTE as HOST_ATTACHMENT_ROUTE } from '../../src/host/attachment'
+import { BACKFILL_ROUTE as HOST_BACKFILL_ROUTE } from '../../src/host/backfill'
+import { FLEET_ROUTE as HOST_FLEET_ROUTE } from '../../src/host/fleet'
+import { SKILLS_ROUTE as HOST_SKILLS_ROUTE } from '../../src/host/skills'
+import {
+  ATTACHMENT_ROUTE,
+  BACKFILL_ROUTE,
+  BALANCE_ROUTE,
+  DETAIL_ROUTE,
+  FLEET_ROUTE,
+  SKILLS_ROUTE,
+} from '../../src/client/apiRoutes'
+
+describe('apiRoutePairing', () => {
+  test('each client fetch route is its host registration minus the leading slash', () => {
+    for (const [host, client] of [
+      [HOST_DETAIL_ROUTE, DETAIL_ROUTE],
+      [HOST_BALANCE_ROUTE, BALANCE_ROUTE],
+      [HOST_FLEET_ROUTE, FLEET_ROUTE],
+      [HOST_SKILLS_ROUTE, SKILLS_ROUTE],
+      [HOST_BACKFILL_ROUTE, BACKFILL_ROUTE],
+      [HOST_ATTACHMENT_ROUTE, ATTACHMENT_ROUTE],
+    ]) {
+      assert.equal(client, host.slice(1), `${host} and ${client} lost their pairing`)
+    }
+  })
+})