diff --git a/.github/workflows/ssh-relay-runtime-artifacts.yml b/.github/workflows/ssh-relay-runtime-artifacts.yml
index 4541f8301c2..3cf63d7a535 100644
--- a/.github/workflows/ssh-relay-runtime-artifacts.yml
+++ b/.github/workflows/ssh-relay-runtime-artifacts.yml
@@ -264,6 +264,7 @@ jobs:
             src/main/ssh/ssh-relay-artifact-selector.test.ts \
             src/main/ssh/ssh-relay-libc-detection.test.ts \
             src/main/ssh/ssh-relay-linux-kernel-detection.test.ts \
+            src/main/ssh/ssh-relay-host-evidence-detection.test.ts \
             src/main/ssh/ssh-relay-darwin-version-detection.test.ts \
             src/main/ssh/ssh-relay-darwin-translation-detection.test.ts \
             src/main/ssh/ssh-relay-linux-libstdcxx-detection.test.ts \
@@ -815,6 +816,7 @@ jobs:
             src/main/ssh/ssh-relay-artifact-selector.test.ts `
             src/main/ssh/ssh-relay-libc-detection.test.ts `
             src/main/ssh/ssh-relay-linux-kernel-detection.test.ts `
+            src/main/ssh/ssh-relay-host-evidence-detection.test.ts `
             src/main/ssh/ssh-relay-darwin-version-detection.test.ts `
             src/main/ssh/ssh-relay-darwin-translation-detection.test.ts `
             src/main/ssh/ssh-relay-linux-libstdcxx-detection.test.ts `
diff --git a/config/scripts/ssh-relay-runtime-workflow.test.mjs b/config/scripts/ssh-relay-runtime-workflow.test.mjs
index e5055c9dd7a..81348800f38 100644
--- a/config/scripts/ssh-relay-runtime-workflow.test.mjs
+++ b/config/scripts/ssh-relay-runtime-workflow.test.mjs
@@ -122,6 +122,7 @@ describe('SSH relay runtime artifact workflow', () => {
       'ssh-relay-artifact-selector.test.ts',
       'ssh-relay-libc-detection.test.ts',
       'ssh-relay-linux-kernel-detection.test.ts',
+      'ssh-relay-host-evidence-detection.test.ts',
       'ssh-relay-darwin-version-detection.test.ts',
       'ssh-relay-darwin-translation-detection.test.ts',
       'ssh-relay-linux-libstdcxx-detection.test.ts',
diff --git a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist-summary.md b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist-summary.md
index 6e8f935c9d6..08c622088dc 100644
--- a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist-summary.md
+++ b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist-summary.md
@@ -9,9 +9,9 @@ keeps commands, hashes, runner identities, timings, and failure details.
 A checked box means the work has evidence in the detailed ledger. Design approval alone does not
 complete a box.
 
-Active checkpoint: **Milestone 5 / Work Package 4 desktop resolver/cache — audit the smallest
-disconnected full host-evidence composition boundary after native acceptance of every individual
-compatibility detector, 2026-07-15, Codex implementation owner.**
+Active checkpoint: **Milestone 5 / Work Package 4 desktop resolver/cache — disconnected host-
+evidence composition is locally green; exact-head all-six native CI is next, 2026-07-15, Codex
+implementation owner.**
 `E-M5-ARTIFACT-CACHE-RESOLUTION-CI-001` closes warm-cache commit
 `22031fa68` on all six native clients, both Linux supplements, Windows x64 baseline, PR Checks,
 Golden E2E, and computer-use; Windows arm64 remains the expected build-26200 rejection against 26100. `E-M5-ARTIFACT-CACHE-RESOLUTION-LOCAL-001` passes 9/9 purpose tests,
@@ -269,6 +269,25 @@ format, max-lines, diff, and protected-resolver gates pass; replacement native C
 clients, both Linux supplements, Windows x64 baseline, PR Checks, Golden E2E, and computer-use pass.
 Both Windows architectures pass all 32 detector cases under native Windows PowerShell. Windows
 arm64 completes full runtime proof and retains only the declared hosted build-26200 rejection against 26100. No live SSH, composer, product caller, setting/fallback, tuple, publication, or default exists.
+`E-M5-HOST-EVIDENCE-COMPOSITION-AUDIT-001` fixes the next disconnected boundary: consume an explicit
+canonical detected platform, SSH connection, and signal; run only that OS family's already-proven
+detectors with at most three concurrent bounded channels; and return frozen selector-shaped evidence.
+Darwin translation unknown returns no evidence rather than inventing native/translated state.
+Inconsistent platform identity, product/startup callers, selector changes, live SSH, settings,
+fallback, transfer/install, tuple enablement, publication, defaults, and SignPath stay absent.
+RED is recorded before implementation: the purpose suite exits 1 because its module is absent
+(0 tests, 316 ms, 132,235,264-byte max RSS), and the workflow oracle exits 1 because the suite has
+only its POSIX native-family occurrence (6 passed/1 failed, 409 ms, 131,743,744-byte max RSS).
+Pre-RED diff and protected-resolver checks pass.
+`E-M5-HOST-EVIDENCE-COMPOSITION-LOCAL-001` is green: 20/20 purpose and 193/193 focused assertions,
+512/512 broader relay assertions, 280/280 release-script assertions, typecheck, lint, format,
+max-lines, diff, no-product-import, and protected-resolver gates pass. The disconnected composer
+validates canonical platform identity before probes; invokes only Linux's three, Darwin's two, or
+Windows' one accepted bounded detector; runs multi-probe families concurrently; preserves
+conservative unknowns; refuses unknown Darwin translation; propagates cancellation/errors; and
+deeply freezes evidence. It is required in both native workflow families. Exact-head all-six Node 24
+client proof remains mandatory; no live SSH, product caller, settings/fallback, transfer/install,
+tuple, publication, default, or SignPath work is included.
 `E-M5-ARTIFACT-CACHE-ROOT-CI-001` closes the pure cache-root contract at exact head `aefcaa9a9`:
 all six primary native Node 24 jobs, both Linux supplements, Windows x64 baseline, PR Checks, Golden
 E2E, and computer-use pass; Windows arm64 build 26200 remains correctly gated against 26100. The
diff --git a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
index c01b7e9fb07..7d61e908426 100644
--- a/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
+++ b/docs/reference/plans/2026-07-14-ssh-relay-github-release-implementation-checklist.md
@@ -8,8 +8,8 @@ work; keep exact commands, runner identities, hashes, metrics, and residual gaps
 
 Date created: 2026-07-14<br>
 Last updated: 2026-07-15<br>
-Current phase: Milestone 5 / Work Package 4 desktop resolver/cache — **In progress — 2026-07-15, Codex implementation owner: audit the smallest disconnected full host-evidence composition boundary after native acceptance of every individual detector**. Keep every capability disconnected from every production/default SSH path. Real Apple/SignPath rehearsals remain an explicit late gate and are not on this package's critical path.<br>
-Session checkpoint: **WINDOWS COMPATIBILITY CI CLOSED / HOST COMPOSITION AUDIT NEXT — 2026-07-15, Codex implementation owner** — `E-M5-WINDOWS-COMPATIBILITY-DETECTION-CI-001` proves both native Windows architectures pass the strict detector, all six primary clients and both Linux supplements pass, Windows x64 baseline passes, and Windows arm64 retains only the declared build-26200/26100 runner mismatch after full runtime proof. Audit only the next disconnected composition boundary; do not add a product caller, settings/fallback wiring, tuple enablement, publication, or default behavior. Merging to `main` remains prohibited, SignPath is deferred, and legacy remains the production default.<br>
+Current phase: Milestone 5 / Work Package 4 desktop resolver/cache — **In progress — 2026-07-15, Codex implementation owner: disconnected host-evidence composition is locally green; exact-head native CI is the next gate**. Keep every capability disconnected from every production/default SSH path. Real Apple/SignPath rehearsals remain an explicit late gate and are not on this package's critical path.<br>
+Session checkpoint: **HOST COMPOSITION LOCAL GREEN / NATIVE CI NEXT — 2026-07-15, Codex implementation owner** — `E-M5-HOST-EVIDENCE-COMPOSITION-LOCAL-001` proves canonical six-tuple mapping, conservative unknowns, Darwin translation policy, bounded concurrency, cancellation/error propagation, deep freezing, workflow-family inclusion, and all local static/broad/release gates. Commit and push this isolated package, then require exact-head all-six native client proof before accepting it or opening another package. Do not add a product caller, settings/fallback wiring, tuple enablement, publication, or default behavior. Merging to `main` remains prohibited, SignPath is deferred, and legacy remains the production default.<br>
 Primary design: [SSH relay GitHub Release plan](./2026-07-14-ssh-relay-github-release-plan.html)<br>
 Motivating issues: [#8450](https://github.com/stablyai/orca/issues/8450), [#1693](https://github.com/stablyai/orca/issues/1693)
 
@@ -147,11 +147,10 @@ same change as the work it records.
   local gates, and all-six native Node 24 proof are green under
   E-M5-ARTIFACT-CACHE-ROOT-LOCAL-RED-001, E-M5-ARTIFACT-CACHE-ROOT-LOCAL-001, and
   E-M5-ARTIFACT-CACHE-ROOT-CI-001. No Electron or product caller exists.
-- Active package: **In progress — 2026-07-15, Codex implementation owner** — audit the smallest
-  disconnected full host-evidence composition boundary after
-  E-M5-WINDOWS-COMPATIBILITY-DETECTION-CI-001 closes every individual detector on native clients.
-  Keep live SSH, transfer/install, settings, fallback wiring, tuple enablement, publication,
-  defaults, and SignPath separately gated.
+- Active package: **In progress — 2026-07-15, Codex implementation owner** — disconnected full host-
+  evidence composition is locally green under E-M5-HOST-EVIDENCE-COMPOSITION-LOCAL-001. Exact-head
+  all-six native client proof is the next acceptance gate. Keep live SSH, transfer/install,
+  settings, fallback wiring, tuple enablement, publication, defaults, and SignPath separately gated.
 - Completed Work Package 2 gate: target-native Windows source-signature reports from exact-head
   artifact jobs 87267322867 and 87267322870 were independently downloaded and matched to their
   identities and signing-stage reports under E-M3-WINDOWS-SOURCE-SIGNATURE-CI-001. PR Checks
@@ -15926,6 +15925,108 @@ config/scripts/ssh-relay-runtime-workflow.test.mjs` — PASS, two files, 38 pass
   tuple enablement, release publication, defaults, and SignPath remain absent. Legacy remains the
   sole production/default path and every tuple stays disabled.
 
+### E-M5-HOST-EVIDENCE-COMPOSITION-AUDIT-001 — disconnected platform-specific evidence composition
+
+- Date/owner: 2026-07-15, Codex implementation owner.
+- Audit: complete reads of the canonical remote-platform type/detector and tests, all six accepted
+  platform-specific compatibility detectors and purpose suites, selector host-evidence union and
+  conservative legacy classifications, native workflow commands/oracle, and the current production-
+  caller graph. The detector functions remain imported only by purpose tests and no host composer
+  exists. The existing platform detector has no cancellation input and must remain unchanged here.
+- Finding: add one purpose-named `ssh-relay-host-evidence-detection` module consuming an explicit
+  already-detected `RemoteHostPlatform`, SSH connection, and optional cancellation signal. First
+  require the platform object's relay-platform identity to agree with its canonical OS/architecture;
+  inconsistent input returns undefined without a probe. Then invoke only the accepted detector family:
+  Linux kernel/libc/libstdc++ concurrently (at most three channels), Darwin version/translation
+  concurrently (at most two), or the single Windows compatibility detector. Return a deeply frozen
+  `SshRelayHostEvidence` object with canonical OS/architecture.
+- Conservative mapping: Linux and Windows are not subject to the reviewed Darwin/Rosetta process-
+  translation policy, so their composed `processTranslated` value is false. Linux preserves
+  `{ family: 'unknown' }` and missing optional fields for later selector classification. A missing
+  complete Windows segment yields Windows evidence with all optional compatibility fields absent so
+  selection remains legacy. Darwin preserves explicit true/false translation and optional version;
+  unknown translation returns no host evidence because inventing either boolean could select a native
+  artifact or misdiagnose a translated process. No selector/type change is needed.
+- Failure/concurrency contract: pass the exact signal to every invoked detector. Pre-abort and
+  `AbortError` propagate; unexpected detector rejection propagates unchanged rather than becoming
+  fallback eligibility. Ordinary probe failures retain each accepted detector's existing unknown
+  return. All OS-specific calls start before composition awaits their results, bounding the composed
+  probe to the slowest existing 15-second detector instead of their sum. No unsupported detector,
+  platform re-probe, retry, network/download, Node, or filesystem operation is introduced.
+- Required RED/green proof: canonical Linux/Darwin/Windows x64 and arm64 mapping; exact detector
+  family/call count; complete and missing/unknown fields; native/translated/unknown Darwin behavior;
+  inconsistent platform rejection with zero probes; deep freezing; all relevant calls starting
+  concurrently; exact signal forwarding; cancellation/unexpected rejection propagation; absence of
+  production imports; and both native workflow families requiring the purpose suite.
+- Deliberately absent: platform-detection modification, full startup/official-manifest/cache
+  orchestration, live SSH/remote cells, semantic transfer capability, transfer/install, settings,
+  fallback classification/wiring, Electron, `ORCA_RELAY_PATH`, tuple enablement, publication,
+  defaults, and SignPath. Legacy remains the sole production/default path and every tuple stays
+  disabled.
+- RED evidence, 2026-07-15:
+  - `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts --maxWorkers=1
+src/main/ssh/ssh-relay-host-evidence-detection.test.ts` — EXPECTED FAIL, exit 1: purpose suite
+    could not import absent `ssh-relay-host-evidence-detection`; zero tests collected in 316 ms,
+    1.76 s wall time, 132,235,264-byte maximum RSS, 96,490,992-byte peak memory footprint.
+  - `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts --maxWorkers=1
+config/scripts/ssh-relay-runtime-workflow.test.mjs` — EXPECTED FAIL, exit 1: 6 passed and the
+    native-family inclusion oracle failed because the purpose suite had only the POSIX workflow
+    occurrence (`source.split(...)` length 2 instead of 3); 409 ms suite duration, 1.84 s wall time,
+    131,743,744-byte maximum RSS, 95,851,800-byte peak memory footprint.
+  - Scope check before RED: `git diff --check` passed; protected
+    `ssh-remote-node-resolution.ts` and `.test.ts` diff remained empty. No implementation or product
+    caller existed.
+
+### E-M5-HOST-EVIDENCE-COMPOSITION-LOCAL-001 — bounded immutable host evidence is locally green
+
+- Date/owner/environment: 2026-07-15, Codex implementation owner; local macOS arm64, Node 26.0.0,
+  pnpm 10.24.0, atop pushed head `cfe56d0fd` plus this isolated uncommitted package. The expected
+  Node-24 engine warning means exact Node 24 remains a native CI gate.
+- Implementation: the new 92-line `ssh-relay-host-evidence-detection.ts` accepts only an explicit
+  already-detected platform, connection, and optional signal. It rejects canonical OS/architecture
+  inconsistency before any probe; starts only the selected OS family's accepted bounded detectors;
+  runs Linux's three and Darwin's two probes concurrently; preserves Linux/Windows unknowns for
+  conservative legacy selection; refuses to invent Darwin translation; propagates cancellation and
+  unexpected rejection; and returns deeply frozen selector-shaped evidence. It has no production
+  import or caller.
+- Purpose command: `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts
+--maxWorkers=1 src/main/ssh/ssh-relay-host-evidence-detection.test.ts` — PASS, one file / 20 tests in
+  337 ms Vitest, 1.69 seconds wall, 132,431,872-byte maximum RSS, zero swaps. It covers all six
+  canonical tuples and exact family call counts, full/unknown/missing mapping, native/translated/
+  unknown Darwin behavior, inconsistent input with zero probes, deep freezing, concurrency, exact
+  signal forwarding, cancellation, and unexpected rejection.
+- Workflow-oracle command: `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts
+--maxWorkers=1 config/scripts/ssh-relay-runtime-workflow.test.mjs` — PASS, one file / seven tests in
+  384 ms Vitest, 1.73 seconds wall, 132,972,544-byte maximum RSS, zero swaps. The purpose suite now
+  occurs exactly once in both POSIX and PowerShell native contract commands.
+- Post-format focused command: `/usr/bin/time -l pnpm exec vitest run --config
+config/vitest.config.ts --maxWorkers=1` plus the composer, Windows compatibility, libc, kernel,
+  Darwin version/translation, libstdc++, selector, platform detection, and workflow-oracle suites —
+  PASS, 10 files / 193 passed / one declared native-Windows skip in 4.66 seconds Vitest, 7.18 seconds
+  wall, 138,493,952-byte maximum RSS, zero swaps.
+- Broader relay command: `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts
+--maxWorkers=1 --silent=true src/main/ssh/ssh-relay-*.test.ts` — PASS, 39 files passed / three
+  declared skipped files, 512 tests passed / four declared platform skips in 25.68 seconds Vitest,
+  27.42 seconds wall, 281,608,192-byte maximum RSS, zero swaps. Only the established stale-lock
+  diagnostic and local Node 26 `module.register()` deprecation warning appear.
+- Release-script command: `/usr/bin/time -l pnpm exec vitest run --config config/vitest.config.ts
+--maxWorkers=1 --silent=true config/scripts/ssh-relay-runtime-*.test.mjs` — PASS, 50 files / 280 tests
+  in 24.51 seconds Vitest, 27.61 seconds wall, 188,825,600-byte maximum RSS, zero swaps.
+- Static gates: `/usr/bin/time -l pnpm typecheck` passes in 5.81 seconds wall with
+  1,262,075,904-byte maximum RSS. `/usr/bin/time -l pnpm lint` passes in 27.03 seconds wall with
+  2,034,597,888-byte maximum RSS; all switch-exhaustiveness, 41 reliability, 355-entry max-lines,
+  bundled-skill, 9,837 localization-reference, locale-parity, and zero-candidate localization gates
+  pass, with the existing 26 warnings only in untouched files. Explicit max-lines, targeted
+  `oxlint`, targeted `oxfmt --check`, `git diff --check`, no-production-import, and protected-
+  resolver empty-diff checks pass. The 92-line implementation and 229-line purpose suite add no
+  max-lines suppression or vague module.
+- Boundary/residual gaps: this is local mock/composition proof, not live SSH or native detector
+  execution. Exact-head all-six Node 24 client proof is mandatory next. Platform detection,
+  manifest/cache startup composition, live SSH/remote cells, semantic transfer capability,
+  transfer/install, Electron/settings, fallback classification/wiring, `ORCA_RELAY_PATH`, tuple
+  enablement, publication, defaults, and SignPath remain absent. Legacy remains the sole production/
+  default path and every tuple stays disabled.
+
 ## Accepted Gaps
 
 No product gap is accepted merely because it appears in this list. Each entry requires explicit
@@ -15984,10 +16085,10 @@ The project is not complete until every applicable item below is checked with ev
 
 ## Next Required Action
 
-Audit only the smallest disconnected Windows compatibility-evidence boundary for the already-reviewed
-OS build, OpenSSH for Windows, Windows PowerShell, and .NET Framework selector fields. Record the
-exact acquisition/parsing/failure contract before adding purpose tests or implementation. Do not
-compose full host evidence, provision production secrets or environments, add an Electron/startup
+Commit and push only the locally green disconnected host-evidence composition package under
+E-M5-HOST-EVIDENCE-COMPOSITION-LOCAL-001, then require exact-head all-six Node 24 native client proof
+and adjacent PR checks before accepting it or auditing the next package. Do not modify platform
+detection or selectors, provision production secrets or environments, add an Electron/startup
 consumer, embed unreviewed keys or manifest bytes, add SSH transfer/install, mode wiring, fallback,
 tuple enablement, release publication, or default behavior.
 Keep Node upstream `.tar.xz` inputs, Windows ZIP, `ORCA_RELAY_PATH`, existing desktop required-assets
diff --git a/src/main/ssh/ssh-relay-host-evidence-detection.test.ts b/src/main/ssh/ssh-relay-host-evidence-detection.test.ts
new file mode 100644
index 00000000000..130f62c54ad
--- /dev/null
+++ b/src/main/ssh/ssh-relay-host-evidence-detection.test.ts
@@ -0,0 +1,229 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import type { SshConnection } from './ssh-connection'
+import { detectSshRelayHostEvidence } from './ssh-relay-host-evidence-detection'
+import { getRemoteHostPlatform, type RemoteHostPlatform } from './ssh-remote-platform'
+
+const detectorMocks = vi.hoisted(() => ({
+  kernel: vi.fn(),
+  libc: vi.fn(),
+  libstdcxx: vi.fn(),
+  darwinVersion: vi.fn(),
+  darwinTranslation: vi.fn(),
+  windowsCompatibility: vi.fn()
+}))
+
+vi.mock('./ssh-relay-linux-kernel-detection', () => ({
+  detectSshRelayLinuxKernelRelease: detectorMocks.kernel
+}))
+vi.mock('./ssh-relay-libc-detection', () => ({
+  detectSshRelayLinuxLibc: detectorMocks.libc
+}))
+vi.mock('./ssh-relay-linux-libstdcxx-detection', () => ({
+  detectSshRelayLinuxLibstdcxx: detectorMocks.libstdcxx
+}))
+vi.mock('./ssh-relay-darwin-version-detection', () => ({
+  detectSshRelayDarwinVersion: detectorMocks.darwinVersion
+}))
+vi.mock('./ssh-relay-darwin-translation-detection', () => ({
+  detectSshRelayDarwinProcessTranslation: detectorMocks.darwinTranslation
+}))
+vi.mock('./ssh-relay-windows-compatibility-detection', () => ({
+  detectSshRelayWindowsCompatibility: detectorMocks.windowsCompatibility
+}))
+
+const connection = {} as SshConnection
+
+beforeEach(() => {
+  vi.resetAllMocks()
+  detectorMocks.kernel.mockResolvedValue('6.8.0-63-generic')
+  detectorMocks.libc.mockResolvedValue({ family: 'glibc', version: '2.39' })
+  detectorMocks.libstdcxx.mockResolvedValue({
+    libstdcxxVersion: '6.0.33',
+    glibcxxVersion: '3.4.33'
+  })
+  detectorMocks.darwinVersion.mockResolvedValue('15.5')
+  detectorMocks.darwinTranslation.mockResolvedValue(false)
+  detectorMocks.windowsCompatibility.mockResolvedValue({
+    build: 26100,
+    openSshVersion: '9.8p1',
+    powerShellVersion: '5.1',
+    dotNetFrameworkRelease: 533325
+  })
+})
+
+function allDetectorCallCounts(): number[] {
+  return Object.values(detectorMocks).map((mock) => mock.mock.calls.length)
+}
+
+describe('SSH relay host evidence detection', () => {
+  it.each([
+    ['linux-x64', 'linux', 'x64', [1, 1, 1, 0, 0, 0]],
+    ['linux-arm64', 'linux', 'arm64', [1, 1, 1, 0, 0, 0]],
+    ['darwin-x64', 'darwin', 'x64', [0, 0, 0, 1, 1, 0]],
+    ['darwin-arm64', 'darwin', 'arm64', [0, 0, 0, 1, 1, 0]],
+    ['win32-x64', 'win32', 'x64', [0, 0, 0, 0, 0, 1]],
+    ['win32-arm64', 'win32', 'arm64', [0, 0, 0, 0, 0, 1]]
+  ] as const)(
+    'maps canonical %s and invokes only its detector family',
+    async (relayPlatform, os, architecture, expectedCalls) => {
+      const result = await detectSshRelayHostEvidence(
+        getRemoteHostPlatform(relayPlatform),
+        connection
+      )
+
+      expect(result).toMatchObject({ os, architecture, processTranslated: false })
+      expect(allDetectorCallCounts()).toEqual(expectedCalls)
+    }
+  )
+
+  it('composes complete Linux evidence and deeply freezes owned values', async () => {
+    const result = await detectSshRelayHostEvidence(getRemoteHostPlatform('linux-x64'), connection)
+
+    expect(result).toEqual({
+      os: 'linux',
+      architecture: 'x64',
+      processTranslated: false,
+      kernelVersion: '6.8.0-63-generic',
+      libc: { family: 'glibc', version: '2.39' },
+      libstdcxxVersion: '6.0.33',
+      glibcxxVersion: '3.4.33'
+    })
+    expect(Object.isFrozen(result)).toBe(true)
+    expect(result?.os === 'linux' && Object.isFrozen(result.libc)).toBe(true)
+  })
+
+  it('preserves unknown Linux libc and missing optional detector evidence', async () => {
+    detectorMocks.kernel.mockResolvedValue(undefined)
+    detectorMocks.libc.mockResolvedValue({ family: 'unknown' })
+    detectorMocks.libstdcxx.mockResolvedValue(undefined)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('linux-arm64'), connection)
+    ).resolves.toEqual({
+      os: 'linux',
+      architecture: 'arm64',
+      processTranslated: false,
+      libc: { family: 'unknown' }
+    })
+  })
+
+  it.each([false, true])('preserves Darwin process translation %s', async (translated) => {
+    detectorMocks.darwinTranslation.mockResolvedValue(translated)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('darwin-arm64'), connection)
+    ).resolves.toEqual({
+      os: 'darwin',
+      architecture: 'arm64',
+      processTranslated: translated,
+      version: '15.5'
+    })
+  })
+
+  it('keeps a known Darwin translation result when the version is unavailable', async () => {
+    detectorMocks.darwinVersion.mockResolvedValue(undefined)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('darwin-x64'), connection)
+    ).resolves.toEqual({
+      os: 'darwin',
+      architecture: 'x64',
+      processTranslated: false
+    })
+  })
+
+  it('returns no Darwin evidence when process translation is unknown', async () => {
+    detectorMocks.darwinTranslation.mockResolvedValue(undefined)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('darwin-arm64'), connection)
+    ).resolves.toBeUndefined()
+  })
+
+  it('preserves complete Windows compatibility evidence', async () => {
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('win32-arm64'), connection)
+    ).resolves.toEqual({
+      os: 'win32',
+      architecture: 'arm64',
+      processTranslated: false,
+      build: 26100,
+      openSshVersion: '9.8p1',
+      powerShellVersion: '5.1',
+      dotNetFrameworkRelease: 533325
+    })
+  })
+
+  it('returns conservative Windows evidence when compatibility detection is unavailable', async () => {
+    detectorMocks.windowsCompatibility.mockResolvedValue(undefined)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('win32-x64'), connection)
+    ).resolves.toEqual({
+      os: 'win32',
+      architecture: 'x64',
+      processTranslated: false
+    })
+  })
+
+  it('rejects inconsistent platform identity without starting any detector', async () => {
+    const inconsistent = {
+      ...getRemoteHostPlatform('linux-x64'),
+      os: 'win32'
+    } as RemoteHostPlatform
+
+    await expect(detectSshRelayHostEvidence(inconsistent, connection)).resolves.toBeUndefined()
+    expect(allDetectorCallCounts()).toEqual([0, 0, 0, 0, 0, 0])
+  })
+
+  it.each([
+    ['linux-x64', ['kernel', 'libc', 'libstdcxx']],
+    ['darwin-x64', ['darwinVersion', 'darwinTranslation']]
+  ] as const)(
+    'starts all %s family probes before awaiting a result',
+    async (relayPlatform, names) => {
+      const settlements = names.map(() => Promise.withResolvers<unknown>())
+      names.forEach((name, index) =>
+        detectorMocks[name].mockReturnValue(settlements[index].promise)
+      )
+
+      const pending = detectSshRelayHostEvidence(getRemoteHostPlatform(relayPlatform), connection)
+
+      expect(names.map((name) => detectorMocks[name].mock.calls.length)).toEqual(names.map(() => 1))
+      settlements.forEach((settlement) => settlement.resolve(undefined))
+      await pending
+    }
+  )
+
+  it('forwards the exact signal to every selected detector', async () => {
+    const controller = new AbortController()
+
+    await detectSshRelayHostEvidence(getRemoteHostPlatform('linux-x64'), connection, {
+      signal: controller.signal
+    })
+
+    for (const mock of [detectorMocks.kernel, detectorMocks.libc, detectorMocks.libstdcxx]) {
+      expect(mock).toHaveBeenCalledWith(connection, { signal: controller.signal })
+    }
+  })
+
+  it('propagates cancellation without converting it to host evidence', async () => {
+    const abortError = new Error('cancel host evidence')
+    abortError.name = 'AbortError'
+    detectorMocks.windowsCompatibility.mockRejectedValue(abortError)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('win32-x64'), connection)
+    ).rejects.toBe(abortError)
+  })
+
+  it('propagates unexpected detector rejection unchanged', async () => {
+    const failure = new Error('unexpected kernel detector failure')
+    detectorMocks.kernel.mockRejectedValue(failure)
+
+    await expect(
+      detectSshRelayHostEvidence(getRemoteHostPlatform('linux-x64'), connection)
+    ).rejects.toBe(failure)
+  })
+})
diff --git a/src/main/ssh/ssh-relay-host-evidence-detection.ts b/src/main/ssh/ssh-relay-host-evidence-detection.ts
new file mode 100644
index 00000000000..deb984e31a1
--- /dev/null
+++ b/src/main/ssh/ssh-relay-host-evidence-detection.ts
@@ -0,0 +1,92 @@
+import type { SshConnection } from './ssh-connection'
+import { detectSshRelayDarwinProcessTranslation } from './ssh-relay-darwin-translation-detection'
+import { detectSshRelayDarwinVersion } from './ssh-relay-darwin-version-detection'
+import { detectSshRelayLinuxLibc } from './ssh-relay-libc-detection'
+import { detectSshRelayLinuxKernelRelease } from './ssh-relay-linux-kernel-detection'
+import { detectSshRelayLinuxLibstdcxx } from './ssh-relay-linux-libstdcxx-detection'
+import { detectSshRelayWindowsCompatibility } from './ssh-relay-windows-compatibility-detection'
+import type { SshRelayHostEvidence } from './ssh-relay-artifact-selector'
+import { getRemoteHostPlatform, type RemoteHostPlatform } from './ssh-remote-platform'
+
+type DetectionOptions = { signal?: AbortSignal }
+
+function isCanonicalPlatform(platform: RemoteHostPlatform): boolean {
+  const canonical = getRemoteHostPlatform(platform.relayPlatform)
+  return canonical.os === platform.os && canonical.arch === platform.arch
+}
+
+async function detectLinuxHostEvidence(
+  platform: RemoteHostPlatform,
+  connection: SshConnection,
+  options: DetectionOptions
+): Promise<SshRelayHostEvidence> {
+  // Why: independent bounded probes run together so composition adds no serial bootstrap latency.
+  const [kernelVersion, libc, libstdcxx] = await Promise.all([
+    detectSshRelayLinuxKernelRelease(connection, options),
+    detectSshRelayLinuxLibc(connection, options),
+    detectSshRelayLinuxLibstdcxx(connection, options)
+  ])
+  const frozenLibc = Object.freeze({ ...libc })
+  return Object.freeze({
+    os: 'linux',
+    architecture: platform.arch,
+    processTranslated: false,
+    ...(kernelVersion === undefined ? {} : { kernelVersion }),
+    libc: frozenLibc,
+    ...(libstdcxx === undefined ? {} : libstdcxx)
+  })
+}
+
+async function detectDarwinHostEvidence(
+  platform: RemoteHostPlatform,
+  connection: SshConnection,
+  options: DetectionOptions
+): Promise<SshRelayHostEvidence | undefined> {
+  const [version, processTranslated] = await Promise.all([
+    detectSshRelayDarwinVersion(connection, options),
+    detectSshRelayDarwinProcessTranslation(connection, options)
+  ])
+  // Why: guessing native or translated could select incompatible executable bytes.
+  if (processTranslated === undefined) {
+    return undefined
+  }
+  return Object.freeze({
+    os: 'darwin',
+    architecture: platform.arch,
+    processTranslated,
+    ...(version === undefined ? {} : { version })
+  })
+}
+
+async function detectWindowsHostEvidence(
+  platform: RemoteHostPlatform,
+  connection: SshConnection,
+  options: DetectionOptions
+): Promise<SshRelayHostEvidence> {
+  const compatibility = await detectSshRelayWindowsCompatibility(connection, options)
+  return Object.freeze({
+    os: 'win32',
+    architecture: platform.arch,
+    processTranslated: false,
+    ...compatibility
+  })
+}
+
+export async function detectSshRelayHostEvidence(
+  platform: RemoteHostPlatform,
+  connection: SshConnection,
+  options: DetectionOptions = {}
+): Promise<SshRelayHostEvidence | undefined> {
+  // Why: inconsistent caller evidence must not start probes or select a runtime for another tuple.
+  if (!isCanonicalPlatform(platform)) {
+    return undefined
+  }
+
+  if (platform.os === 'linux') {
+    return detectLinuxHostEvidence(platform, connection, options)
+  }
+  if (platform.os === 'darwin') {
+    return detectDarwinHostEvidence(platform, connection, options)
+  }
+  return detectWindowsHostEvidence(platform, connection, options)
+}