Enforce real timeouts on gpg subprocess calls (closes #62)

Every gpg run now has a one-minute deadline (gpgTimeout) on top of its
caller's context and is killed when either ends. A timeout is reported
as "gpg timed out" under the failing operation instead of "signal:
killed". Only gpg itself is killed; WaitDelay (one second) stops the run
from waiting on a process gpg left behind that still holds its output,
such as a wrapper script that does not exec the real gpg.
Builder.Build and Checker.ExtractEmbeddedSigningKeyFP take a context, so
ToManifest's context now reaches signing and the contextcheck
suppression calling signing non-cancellable is gone. Manifest loading
takes no context, so its signature check is bounded by the timeout
alone.

Model: opus-5-5

AGENTS.md

@@ -27,8 +27,5 @@ source for coding standards, formatting, linting, and workflow rules.
 - The proto definition is in `mfer/mf.proto`; generated `.pb.go` files are
   committed (required for `go get` compatibility).
 - The format specification is in `FORMAT.md`.
-- Open work, open design questions included, is tracked only in the repo's
-  issues: https://git.eeqj.de/sneak/mfer/issues. There is no `TODO.md` and no
-  TODO list in `README.md`; do not add either. For this repo this overrides the
-  `REPO_POLICIES.md` rule to put the todo list in the README, per sneak's
-  ruling: https://git.eeqj.de/sneak/mfer/issues/76#issuecomment-118130.
+- See the TODO section in `README.md` for the 1.0 implementation plan and open
+  design questions.

README.md

@@ -157,23 +157,18 @@ The manifest file would do several important things:
     - metadata size should not be used as an excuse to sacrifice utility (such
       as providing checksums over each chunk of a large file)
 
-# Original Design Questions
-
-These were the open questions when the project started; open design questions
-are now tracked only in the [issues](https://git.eeqj.de/sneak/mfer/issues).
+# Open Questions
 
 - Should the manifest file include checksums of individual file chunks, or just
-  for the whole assembled file? If so, should the chunk size be fixed or
-  dynamic? Still open, on
-  [issue 81](https://git.eeqj.de/sneak/mfer/issues/81#issuecomment-118698).
+  for the whole assembled file?
+
+    - If so, should the chunksize be fixed or dynamic?
 
 - Should the manifest signature format be GnuPG signatures, or those from
   OpenBSD's signify (of which there is a good
-  [golang implementation](https://github.com/frankbraun/gosignify))? Still open,
-  as question 10 on [issue 82](https://git.eeqj.de/sneak/mfer/issues/82).
+  [golang implementation](https://github.com/frankbraun/gosignify)?
 
-- Should the on-disk serialization format be proto3 or json? Settled: it is
-  proto3, see `FORMAT.md` and `mfer/mf.proto`.
+- Should the on-disk serialization format be proto3 or json?
 
 # Tool Examples
 
@@ -251,10 +246,207 @@ regardless of filesystem format.
 Please email [`sneak@sneak.berlin`](mailto:sneak@sneak.berlin) with your desired
 username for an account on this Gitea instance.
 
-# TODO
+# TODO: Remaining Work for 1.0
 
-Open work, open design questions included, is tracked in this repo's issues:
-[https://git.eeqj.de/sneak/mfer/issues](https://git.eeqj.de/sneak/mfer/issues).
+## Design Questions (Owner Decision Required)
+
+These require @sneak's input before implementation. Answers should be added
+inline below each question.
+
+### Format Design
+
+**1. Should `MFFileChecksum` be simplified?** Currently it's a separate message
+wrapping a single `bytes multiHash` field. Since multihash already
+self-describes the algorithm, `repeated bytes hashes` directly on `MFFilePath`
+would be simpler and reduce per-file protobuf overhead. Is the extra message
+layer intentional (e.g. planning to add per-hash metadata like `verified_at`)?
+
+> _answer:_
+
+**2. Should file permissions/mode be stored?** The format stores mtime/ctime but
+not Unix file permissions. For archival use this may not matter, but for
+software distribution or filesystem restoration it's a gap. Should we reserve a
+field now (e.g. `optional uint32 mode = 305`) even if we don't populate it yet?
+
+> _answer:_
+
+**3. Should `atime` be removed from the schema?** Access time is volatile,
+non-deterministic, and often disabled (`noatime`). Including it means two
+manifests of the same directory at different times will differ, which conflicts
+with the determinism goal. Remove it, or document it as "never set by default"?
+
+> _answer:_
+
+**4. What are the path normalization rules?** The proto has `string path` with
+no specification about: always forward-slash? Must be relative? No `..`
+components allowed? UTF-8 NFC vs NFD normalization (macOS vs Linux)? Max path
+length? This is a security issue (path traversal) and a cross-platform
+compatibility issue. What rules should the spec mandate?
+
+> _answer:_
+
+**5. Should we add a version byte after the magic?** Currently `ZNAVSRFG` is
+followed immediately by protobuf. Adding a version byte (`ZNAVSRFG\x01`) would
+allow future framing changes without requiring protobuf parsing to detect the
+version. `MFFileOuter.Version` serves this purpose but requires successful
+deserialization to read. Worth the extra byte?
+
+> _answer:_
+
+**6. Should we add a length-prefix after the magic?** Protobuf is not
+self-delimiting. If we ever want to concatenate manifests or append data after
+the protobuf, the current framing is insufficient. Add a varint or fixed-width
+length-prefix?
+
+> _answer:_
+
+### Signature Design
+
+**7. What does the outer SHA-256 hash cover — compressed or uncompressed data?**
+The code currently hashes compressed data (good for verifying before
+decompression), but this should be explicitly documented. Which is the intended
+behavior?
+
+> _answer:_
+
+**8. Should `signatureString()` sign raw bytes instead of a hex-encoded
+string?** Currently the canonical string is `MAGIC-UUID-MULTIHASH` with hex
+encoding, which adds a transformation layer. Signing the raw `sha256` bytes (or
+compressed `innerMessage` directly) would be simpler. Keep the string format or
+switch to raw bytes?
+
+> _answer:_
+
+**9. Should we support detached signature files (`.mf.sig`)?** Embedded
+signatures are better for single-file distribution. Detached `.mf.sig` files
+follow the familiar `SHASUMS`/`SHASUMS.asc` pattern and are simpler for HTTP
+serving. Support both modes?
+
+> _answer:_
+
+**10. GPG vs pure-Go crypto for signatures?** Shelling out to `gpg` is fragile
+(may not be installed, version-dependent output).
+`github.com/ProtonMail/go-crypto` provides pure-Go OpenPGP, or we could use
+Ed25519/signify (simpler, no key management). Which direction?
+
+> _answer:_
+
+### Implementation Design
+
+**11. Should manifests be deterministic by default?** This means: sort file
+entries by path, omit `createdAt` timestamp (or make it opt-in), no `atime`.
+Should determinism be the default, with a `--include-timestamps` flag to opt in?
+
+> _answer:_
+
+**12. Should we consolidate or keep both scanner/checker implementations?**
+There are two parallel implementations: `mfer/scanner.go` + `mfer/checker.go`
+(typed with `FileSize`, `RelFilePath`) and `internal/scanner/` +
+`internal/checker/` (raw `int64`, `string`). The `mfer/` versions are superior.
+Delete the `internal/` versions?
+
+> _answer:_
+
+**13. Should the `manifest` type be exported?** Currently unexported with
+exported constructors (`NewManifestFromReader`, `NewManifestFromFile`).
+Consumers can't declare `var m *mfer.manifest`. Export the type, or define an
+interface?
+
+> _answer:_
+
+**14. What should the Go module path be for 1.0?** Currently
+`sneak.berlin/go/mfer` in `go.mod` but `git.eeqj.de/sneak/mfer/mfer` in the
+proto `go_package` option. Which is canonical?
+
+> _answer:_
+
+## Implementation Tasks
+
+### Repo Infrastructure
+
+- [ ] Add `.golangci.yml` (fetch from
+      `https://git.eeqj.de/sneak/prompts/raw/branch/main/.golangci.yml`)
+- [ ] Add `.editorconfig`
+- [ ] Add `.gitea/workflows/check.yml` that runs `docker build .`
+
+### Format & Correctness
+
+- [ ] Resolve proto `go_package` path inconsistency
+      (`git.eeqj.de/sneak/mfer/mfer` vs `sneak.berlin/go/mfer`)
+- [ ] Specify path invariants — add proto comments requiring UTF-8,
+      forward-slash, relative paths, no `..`, no leading `/`; validate in
+      `Builder.AddFile` and `Builder.AddFileWithHash` (pending design question
+      answer)
+- [ ] Remove or deprecate `atime` from proto (pending design question answer)
+- [ ] Reserve `optional uint32 mode = 305` in `MFFilePath` for future file
+      permissions (pending design question answer)
+- [ ] Add version byte after magic — `ZNAVSRFG\x01` for format version 1
+      (pending design question answer)
+- [ ] Write format specification document — separate from README: magic, outer
+      structure, compression, inner structure, path invariants, signature
+      scheme, canonical serialization
+
+### Library
+
+- [ ] Delete `internal/scanner/` and `internal/checker/` — consolidate on
+      `mfer/` package versions; update CLI code (pending design question answer)
+- [ ] Add deterministic file ordering — sort entries by path (lexicographic,
+      byte-order) in `Builder.Build()`; add test asserting byte-identical output
+      from two runs
+- [ ] Add decompression size limit — `io.LimitReader` in `deserializeInner()`
+      with `m.pbOuter.Size` as bound
+- [ ] Fix `errors.Is` dead code in checker — replace with `os.IsNotExist(err)`
+      or `errors.Is(err, fs.ErrNotExist)`
+- [ ] Fix `AddFile` to verify size — check `totalRead == size` after reading,
+      return error on mismatch
+- [ ] Export the `manifest` type or define a public interface (pending design
+      question answer) — currently consumers cannot hold a reference to a loaded
+      manifest in their own type declarations
+- [ ] Replace GPG subprocess calls with pure-Go crypto (pending design question
+      answer) — current implementation shells out to `gpg` which may not be
+      installed
+- [ ] Add timeout to any remaining subprocess calls
+
+### CLI
+
+- [ ] Fix flag naming — all CLI flags should use kebab-case as primary
+      (`--include-dotfiles`, `--follow-symlinks`)
+- [ ] Fix URL construction in fetch — use `BaseURL.JoinPath()` or
+      `url.JoinPath()` instead of string concatenation
+- [ ] Add progress rate-limiting to Checker — throttle to once per second,
+      matching Scanner
+- [ ] Add `--deterministic` flag or make it default — omit `createdAt`, sort
+      files (pending design question answer)
+- [ ] Wire `--version` flag properly (currently only a `version` subcommand
+      exists; top-level `--version` shows urfave/cli generic output)
+- [ ] Add retry logic to `fetch` — currently no retries on transient HTTP
+      errors; needs exponential backoff
+- [ ] `fetch` command uses bare `http.Get` with no timeout — needs `http.Client`
+      with configurable timeout
+
+### Testing & Robustness
+
+- [ ] Add fuzzing tests for `NewManifestFromReader` — protobuf deserialization
+      of untrusted input needs fuzz coverage
+- [ ] Add integration test for `freshen` CLI command — current tests only verify
+      setup, not the actual freshen operation end-to-end
+- [ ] Add test for `fetch` CLI command end-to-end (currently only `downloadFile`
+      is tested)
+
+### Documentation
+
+- [ ] Promote `FORMAT.md` as primary spec reference; README should link to it
+      more prominently
+- [ ] Audit and update all error messages for consistency and helpfulness
+- [ ] Document the signature scheme more thoroughly (canonical string format,
+      verification steps)
+
+### Release
+
+- [ ] Finalize Go module path
+- [ ] Update version constant in `mfer/constants.go`
+- [ ] Add `--version` output matching SemVer
+- [ ] Tag `v1.0.0`
 
 # See Also
 

TODO.md

@@ -0,0 +1,138 @@
+# Workflow
+
+- branch (from `main`)
+- do the work in Next Step
+- move Next Step to the top of Completed Steps
+- move the top item of Future Steps into Next Step
+- commit (`TODO.md` changes in the same commit as the work)
+- merge to `main` if the branch is not protected, otherwise open a PR
+- push
+
+# Status
+
+pre-1.0. No git tags. README section "TODO: Remaining Work for 1.0" lists open
+design questions and implementation tasks; policy compliance work is in flight
+and unmerged.
+
+# Next Step
+
+Work through the remaining compliance items folded from the 2026-07-02 audit
+(the first group under Future Steps): `.editorconfig`, `.gitignore` coverage,
+gofumpt-based `fmt-check`, README "Getting Started", and the rest.
+`.golangci.yml` and `TODO.md` are tracked and committed as of 2026-08-07, so the
+only thing left of the `chore/align-repo-policies` branch is the list below.
+
+# Completed Steps
+
+- 2026-10-03: every gpg run is killed after one minute or when its caller's
+  context ends, and a timeout reads as "gpg timed out" under the failing
+  operation; `Builder.Build` and `Checker.ExtractEmbeddedSigningKeyFP` take a
+  context, which reaches gpg (#62)
+- 2026-10-03: pinned the CLI error messages by driving the functions that emit
+  them in `internal/cli/errmsg_test.go`, and made the freshen mtime-presence
+  test distinguish an absent mtime from the epoch (#87)
+- 2026-10-03: `script/cibuild` builds the image with the same command as
+  `script/docker`, `--no-cache` included, so the checks in the Dockerfile run on
+  every build, also on an unchanged tree (#89)
+- 2026-10-03: `fetch` removes whatever sits at a file's temp name and then
+  creates the temp file only if that name is free, so a hard link left there
+  cannot make it write into a file outside the destination directory (#115)
+- 2026-10-03: `fetch` refuses any manifest path that runs through a symlink
+  already in the destination directory, checked before each of its writes
+  (directories, temp file, rename), so such a symlink cannot send a write
+  outside it (#86)
+- 2026-10-02: a plain `docker build .` of a clone now stamps the tag or short
+  commit into `mfer version` instead of nothing: `.dockerignore` sends `.git`
+  (not `.git/config`), and the build stage takes the `VERSION` build argument,
+  otherwise `git describe --tags --always`, failing if `.git` is present and no
+  version comes out. `script/docker` is the canonical copy, which passes
+  `VERSION`; `bin/gitrev.sh` uses `--tags` too (#112)
+- 2026-09-21: validate manifest entry paths on deserialize so untrusted `.mf`
+  files cannot make `Checker` stat or read outside `basePath` (#61)
+- 2026-09-21: rewrote `script/test` to the canonical pattern (30s timeout,
+  `-race -cover`, quiet-first with verbose-on-failure rerun) and fixed the
+  process-global logger data race it surfaced (#67)
+- 2026-09-21: added the canonical `.editorconfig`, made `.gitignore` cover
+  secrets, OS, editor, and Go artifacts, and removed the dead Drone CI
+  references from `.gitignore` and `bin/gitrev.sh` (#72)
+- 2026-08-09: added `.prettierrc`/`.prettierignore`, gave `script/fmt` and
+  `script/fmt-check` one shared prettier file set via `script/prettier`, dropped
+  the `|| true` that hid prettier failures, and added a node-based Dockerfile
+  stage so a markdown formatting violation fails `docker build .` (#69)
+- 2026-08-07: updated golangci-lint to v2.12.2 everywhere it is pinned
+  (`Makefile`, `Dockerfile`), added the canonical `.golangci.yml`
+  (`default: all`), and fixed all resulting lint findings across the codebase
+- 2026-07-07 Adopted scripts-to-rule-them-all: `script/` entrypoints, Makefile
+  shims, README Entrypoints section
+- 2026-07-03: aligned repo tooling, docs, and config with standardized policies
+  (7d9a138, on chore/align-repo-policies, unmerged)
+- 2026-06-28: moved to standardized repo policies (#56, on main)
+- 2026-04-07: added 1.0 roadmap as README TODO section, removed old TODO.md
+  (#54)
+- 2026-03-20: added Gitea Actions CI workflow (#53)
+- 2026-03-17: added REPO_POLICIES.md, renamed CLAUDE.md to AGENTS.md (#51);
+  removed committed .index.mf (#52)
+- 2026-03-15: split Dockerfile with pre-built golangci-lint stage for faster CI
+  (#45)
+- 2026-03-01: 1.0 quality polish: code review, tests, bug fixes, docs (#32)
+- 2026-02-20: deterministic file ordering in Builder.Build() (#28); removed
+  committed vendor/modcache archives (#35)
+- 2026-02-08: added --seed flag for deterministic manifest UUID
+
+# Future Steps
+
+- Compliance (fold of TODO.md audit 2026-07-02; verify which items the in-flight
+  branch already closes, then check off):
+    - Add .editorconfig (canonical copy from sneak/prompts)
+    - Make .gitignore cover secrets (.env, _.key, _.pem), OS files (.DS_Store),
+      and editor files (_.swp, _~)
+    - Make fmt-check/lint verify with gofumpt, not gofmt -l, so `make check`
+      matches what `make fmt` writes
+    - Add README "Getting Started" section with copy-pasteable install/usage
+      block
+    - Move FORMAT.md from repo root to docs/ and update the AGENTS.md reference
+    - Pin Makefile-installed Go tools (`protoc-gen-go@v1.28.1`,
+      `golangci-lint@v2.12.2`) by module hash, not mutable tag
+    - Add explicit README "Rationale" heading (content exists under other
+      names); name the author in the README Description first line
+    - Reconcile root-level AGENTS.md with directory-hygiene policy (keep or
+      relocate)
+    - Add a `make build` target
+    - Rewrite `make hooks` to use printf or a heredoc instead of non-portable
+      `echo '...\n...'`
+- Answer the 14 owner design questions in the README 1.0 roadmap:
+    - Format: simplify MFFileChecksum; store file mode; drop atime; specify path
+      normalization rules; version byte after magic; length-prefix after magic
+    - Signatures: hash covers compressed or uncompressed data; sign raw bytes vs
+      hex canonical string; detached .mf.sig support; GPG subprocess vs pure-Go
+      crypto
+    - Implementation: deterministic manifests by default; consolidate duplicate
+      scanner/checker implementations; export the manifest type; canonical Go
+      module path for 1.0
+- Format and correctness:
+    - Resolve proto go_package vs go.mod module path inconsistency
+    - Specify and validate path invariants (UTF-8, forward-slash, relative, no
+      .., no leading /)
+    - Remove or deprecate atime; reserve mode field; add version byte (all
+      pending design answers)
+    - Write a standalone format specification document
+- Library:
+    - Delete internal/scanner and internal/checker; consolidate on the mfer/
+      package versions (pending design answer)
+    - Add decompression size limit via io.LimitReader in deserializeInner()
+    - Fix errors.Is dead code in checker; make AddFile verify totalRead == size
+    - Export manifest type or define a public interface (pending)
+    - Replace GPG subprocess with pure-Go crypto (pending)
+- CLI:
+    - Kebab-case primary flag names; fix fetch URL construction with
+      url.JoinPath; add http.Client timeout and retry with backoff to fetch;
+      rate-limit Checker progress output; add --deterministic flag or default;
+      wire top-level --version properly
+- Testing:
+    - Fuzz NewManifestFromReader; end-to-end tests for freshen and fetch
+- Documentation:
+    - Promote docs/FORMAT.md as primary spec reference; audit error messages;
+      document the signature scheme fully
+- Release:
+    - Finalize module path, bump version constant, SemVer --version output, tag
+      v1.0.0

internal/cli/check.go

@@ -2,6 +2,7 @@
 package cli
 
 import (
+	"context"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -126,7 +127,9 @@ func (mfa *CLIApp) fetchManifestToTemp(url string) (string, error) {
 
 // verifyRequiredSigner enforces the --require-signature fingerprint
 // against the manifest's embedded signing key.
-func verifyRequiredSigner(chk *mfer.Checker, requiredSigner string) error {
+func verifyRequiredSigner(
+	ctx context.Context, chk *mfer.Checker, requiredSigner string,
+) error {
 	// Validate fingerprint format: must be exactly 40 hex characters
 	if len(requiredSigner) != fingerprintHexLen {
 		return fmt.Errorf("%w, got %d", errInvalidFingerprint, len(requiredSigner))
@@ -145,7 +148,7 @@ func verifyRequiredSigner(chk *mfer.Checker, requiredSigner string) error {
 	// Extract fingerprint from the embedded public key (not from the
 	// signer field). This validates the key is importable and gets its
 	// actual fingerprint.
-	embeddedFP, err := chk.ExtractEmbeddedSigningKeyFP()
+	embeddedFP, err := chk.ExtractEmbeddedSigningKeyFP(ctx)
 	if err != nil {
 		return fmt.Errorf(
 			"failed to extract fingerprint from embedded signing key: %w", err)
@@ -303,7 +306,7 @@ func (mfa *CLIApp) checkManifestOperation(ctx *cli.Context) error {
 	// Check signature requirement
 	requiredSigner := ctx.String("require-signature")
 	if requiredSigner != "" {
-		err = verifyRequiredSigner(chk, requiredSigner)
+		err = verifyRequiredSigner(ctx.Context, chk, requiredSigner)
 		if err != nil {
 			return err
 		}

internal/cli/errmsg_test.go

@@ -83,7 +83,8 @@ func TestVerifyRequiredSignerMessages(t *testing.T) {
 	t.Run("invalid fingerprint length", func(t *testing.T) {
 		t.Parallel()
 
-		err := verifyRequiredSigner(unsignedChecker(t), "12345678")
+		err := verifyRequiredSigner(context.Background(),
+			unsignedChecker(t), "12345678")
 		require.ErrorIs(t, err, errInvalidFingerprint)
 		assert.EqualError(t, err,
 			"invalid fingerprint: must be exactly 40 hex characters, got 8")
@@ -92,7 +93,8 @@ func TestVerifyRequiredSignerMessages(t *testing.T) {
 	t.Run("manifest not signed", func(t *testing.T) {
 		t.Parallel()
 
-		err := verifyRequiredSigner(unsignedChecker(t), msgFpA)
+		err := verifyRequiredSigner(context.Background(),
+			unsignedChecker(t), msgFpA)
 		require.ErrorIs(t, err, errManifestNotSigned)
 		assert.EqualError(t, err,
 			"manifest is not signed, but signature from "+msgFpA+" is required")
@@ -109,10 +111,10 @@ func TestVerifyRequiredSignerMessages(t *testing.T) {
 func TestSignerMismatchMessage(t *testing.T) {
 	chk := signedChecker(t)
 
-	embeddedFP, err := chk.ExtractEmbeddedSigningKeyFP()
+	embeddedFP, err := chk.ExtractEmbeddedSigningKeyFP(context.Background())
 	require.NoError(t, err)
 
-	err = verifyRequiredSigner(chk, msgFpB)
+	err = verifyRequiredSigner(context.Background(), chk, msgFpB)
 	require.ErrorIs(t, err, errSignerMismatch)
 	assert.EqualError(t, err,
 		"embedded signing key fingerprint "+embeddedFP+
@@ -160,7 +162,7 @@ func signedChecker(t *testing.T) *mfer.Checker {
 
 	var buf bytes.Buffer
 
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	fs := afero.NewMemMapFs()
 	require.NoError(t, afero.WriteFile(fs, "/index.mf", buf.Bytes(), 0o644))

internal/cli/freshen.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"context"
 	"crypto/sha256"
 	"errors"
 	"fmt"
@@ -304,7 +305,7 @@ func (h *freshenHasher) processEntry(e *freshenEntry) error {
 // writeFreshenedManifest writes the manifest atomically (write to a
 // temp file, then rename over the target).
 func writeFreshenedManifest(
-	afs afero.Fs, builder *mfer.Builder, manifestPath string,
+	ctx context.Context, afs afero.Fs, builder *mfer.Builder, manifestPath string,
 ) error {
 	tmpPath := manifestPath + ".tmp"
 
@@ -313,7 +314,7 @@ func writeFreshenedManifest(
 		return fmt.Errorf("failed to create temp file: %w", err)
 	}
 
-	err = builder.Build(outFile)
+	err = builder.Build(ctx, outFile)
 	_ = outFile.Close()
 
 	if err != nil {
@@ -530,7 +531,7 @@ func (mfa *CLIApp) freshenManifestOperation(ctx *cli.Context) error {
 	}
 
 	// Write updated manifest atomically (write to temp, then rename)
-	err = writeFreshenedManifest(mfa.Fs, hasher.builder, manifestPath)
+	err = writeFreshenedManifest(ctx.Context, mfa.Fs, hasher.builder, manifestPath)
 	if err != nil {
 		return err
 	}

mfer/builder.go

@@ -3,6 +3,7 @@
 package mfer
 
 import (
+	"context"
 	"crypto/sha256"
 	"errors"
 	"fmt"
@@ -281,8 +282,9 @@ func (b *Builder) SetSigningOptions(opts *SigningOptions) {
 	b.signingOptions = opts
 }
 
-// Build finalizes the manifest and writes it to the writer.
-func (b *Builder) Build(w io.Writer) error {
+// Build finalizes the manifest and writes it to the writer. ctx bounds the
+// gpg runs that sign the manifest when signing options are set.
+func (b *Builder) Build(ctx context.Context, w io.Writer) error {
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
@@ -308,13 +310,13 @@ func (b *Builder) Build(w io.Writer) error {
 	}
 
 	// Generate outer wrapper
-	err := m.generateOuter()
+	err := m.generateOuter(ctx)
 	if err != nil {
 		return fmt.Errorf("build: generate outer: %w", err)
 	}
 
 	// Generate final output
-	err = m.generate()
+	err = m.generate(ctx)
 	if err != nil {
 		return fmt.Errorf("build: generate: %w", err)
 	}

mfer/builder_test.go

@@ -3,6 +3,7 @@ package mfer
 
 import (
 	"bytes"
+	"context"
 	"strings"
 	"testing"
 	"time"
@@ -113,7 +114,7 @@ func TestBuilderBuild(t *testing.T) {
 
 	var buf bytes.Buffer
 
-	err = b.Build(&buf)
+	err = b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Should have magic bytes
@@ -177,7 +178,7 @@ func TestBuilderDeterministicOutput(t *testing.T) {
 
 		var buf bytes.Buffer
 
-		err := b.Build(&buf)
+		err := b.Build(context.Background(), &buf)
 		require.NoError(t, err)
 
 		return buf.Bytes()
@@ -325,7 +326,7 @@ func TestBuilderBuildRoundTrip(t *testing.T) {
 	}
 
 	var buf bytes.Buffer
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	m, err := NewManifestFromReader(&buf)
 	require.NoError(t, err)
@@ -383,7 +384,7 @@ func TestManifestString(t *testing.T) {
 	require.NoError(t, err)
 
 	var buf bytes.Buffer
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	m, err := NewManifestFromReader(&buf)
 	require.NoError(t, err)
@@ -397,7 +398,7 @@ func TestBuilderBuildEmpty(t *testing.T) {
 
 	var buf bytes.Buffer
 
-	err := b.Build(&buf)
+	err := b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Should still produce valid manifest with 0 files
@@ -416,7 +417,7 @@ func TestBuilderOmitsCreatedAtByDefault(t *testing.T) {
 	require.NoError(t, err)
 
 	var buf bytes.Buffer
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	m, err := NewManifestFromReader(&buf)
 	require.NoError(t, err)
@@ -438,7 +439,7 @@ func TestBuilderIncludesCreatedAtWhenRequested(t *testing.T) {
 	require.NoError(t, err)
 
 	var buf bytes.Buffer
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	m, err := NewManifestFromReader(&buf)
 	require.NoError(t, err)
@@ -464,7 +465,7 @@ func TestBuilderDeterministicFileOrder(t *testing.T) {
 		}
 
 		var buf bytes.Buffer
-		require.NoError(t, b.Build(&buf))
+		require.NoError(t, b.Build(context.Background(), &buf))
 		m, err := NewManifestFromReader(&buf)
 		require.NoError(t, err)
 

mfer/checker.go

@@ -164,12 +164,12 @@ func (c *Checker) SigningPubKey() []byte {
 // ExtractEmbeddedSigningKeyFP imports the manifest's embedded public key into a
 // temporary keyring and extracts its fingerprint. This validates the key and
 // returns its actual fingerprint from the key material itself.
-func (c *Checker) ExtractEmbeddedSigningKeyFP() (string, error) {
+func (c *Checker) ExtractEmbeddedSigningKeyFP(ctx context.Context) (string, error) {
 	if len(c.signingPubKey) == 0 {
 		return "", errNoSigningPubKey
 	}
 
-	return gpgExtractPubKeyFingerprint(c.signingPubKey)
+	return gpgExtractPubKeyFingerprint(ctx, c.signingPubKey)
 }
 
 // Check verifies all files against the manifest.

mfer/checker_test.go

@@ -61,7 +61,7 @@ func createTestManifest(
 	}
 
 	var buf bytes.Buffer
-	require.NoError(t, builder.Build(&buf))
+	require.NoError(t, builder.Build(context.Background(), &buf))
 	require.NoError(t, afero.WriteFile(fs, manifestPath, buf.Bytes(), 0o644))
 }
 

mfer/deserialize.go

@@ -2,6 +2,7 @@ package mfer
 
 import (
 	"bytes"
+	"context"
 	"crypto/sha256"
 	"errors"
 	"fmt"
@@ -92,7 +93,9 @@ func (m *manifest) verifyOuterIntegrity() error {
 		)
 	}
 
+	// Loading a manifest takes no context; gpgTimeout still bounds gpg.
 	err = gpgVerify(
+		context.Background(),
 		[]byte(sigString),
 		m.pbOuter.GetSignature(),
 		m.pbOuter.GetSigningPubKey(),

mfer/deserialize_path_test.go

@@ -3,6 +3,7 @@ package mfer
 
 import (
 	"bytes"
+	"context"
 	"crypto/sha256"
 	"fmt"
 	"testing"
@@ -122,7 +123,7 @@ func TestDeserializeValidManifestRoundTrips(t *testing.T) {
 	require.NoError(t, b.AddFileWithHash("dir/file.txt", 123, ModTime{}, hash))
 
 	var buf bytes.Buffer
-	require.NoError(t, b.Build(&buf))
+	require.NoError(t, b.Build(context.Background(), &buf))
 
 	m, err := NewManifestFromReader(bytes.NewReader(buf.Bytes()))
 	require.NoError(t, err)

mfer/errmsg_test.go

@@ -2,6 +2,7 @@
 package mfer
 
 import (
+	"context"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -80,6 +81,7 @@ func TestSerializeInternalErrorMessagesVerbatim(t *testing.T) {
 	t.Parallel()
 
 	m := &manifest{}
-	require.EqualError(t, m.generate(), "internal error: pbInner not set")
-	require.EqualError(t, m.generateOuter(), "internal error")
+	require.EqualError(t, m.generate(context.Background()),
+		"internal error: pbInner not set")
+	require.EqualError(t, m.generateOuter(context.Background()), "internal error")
 }

mfer/gpg.go

@@ -10,9 +10,21 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"time"
 )
 
 const (
+	// gpgTimeout bounds every gpg run, which can otherwise wait forever on
+	// a passphrase prompt or a stalled gpg-agent. A minute leaves a person
+	// time to type a passphrase or touch a smartcard.
+	gpgTimeout = time.Minute
+
+	// gpgWaitDelay is how long a gpg run keeps waiting for gpg's stdout
+	// and stderr to close once gpg has been killed or has exited. Reading
+	// what gpg itself wrote takes far less; only a process gpg left behind
+	// holds them open longer.
+	gpgWaitDelay = time.Second
+
 	// privateDirPerms is the permission mode for temporary GPG home
 	// directories.
 	privateDirPerms os.FileMode = 0o700
@@ -66,8 +78,20 @@ func gpgArgs(opts []string, positional ...string) []string {
 }
 
 // runGPG runs the gpg binary in batch mode with the given arguments and
-// optional stdin, returning captured stdout and stderr.
-func runGPG(stdin io.Reader, args ...string) (*bytes.Buffer, *bytes.Buffer, error) {
+// optional stdin, returning captured stdout and stderr. gpg is killed when
+// ctx ends or gpgTimeout passes, whichever comes first.
+func runGPG(
+	ctx context.Context, stdin io.Reader, args ...string,
+) (*bytes.Buffer, *bytes.Buffer, error) {
+	// exec.CommandContext kills only gpg itself. A gpg-agent that gpg
+	// starts runs detached and holds none of gpg's output, but another
+	// process gpg leaves behind (a wrapper script that runs the real gpg
+	// without exec, for example) can keep gpg's stdout or stderr open, and
+	// Run would wait for it to exit. WaitDelay stops that wait
+	// gpgWaitDelay after the kill; that process is left running.
+	ctx, cancel := context.WithTimeout(ctx, gpgTimeout)
+	defer cancel()
+
 	fullArgs := append([]string{"--batch", "--no-tty"}, args...)
 
 	// G204: the executable name is a compile-time constant. The arguments
@@ -76,7 +100,8 @@ func runGPG(stdin io.Reader, args ...string) (*bytes.Buffer, *bytes.Buffer, erro
 	// option or after the "--" end-of-options marker inserted by gpgArgs,
 	// and therefore cannot be reinterpreted by gpg as an option.
 	cmd := exec.CommandContext( //nolint:gosec // G204: see comment above
-		context.Background(), "gpg", fullArgs...)
+		ctx, "gpg", fullArgs...)
+	cmd.WaitDelay = gpgWaitDelay
 	cmd.Stdin = stdin
 
 	var stdout, stderr bytes.Buffer
@@ -85,6 +110,14 @@ func runGPG(stdin io.Reader, args ...string) (*bytes.Buffer, *bytes.Buffer, erro
 	cmd.Stderr = &stderr
 
 	err := cmd.Run()
+	if err != nil && ctx.Err() != nil {
+		// gpg was killed because ctx ended, which Run reports only as
+		// "signal: killed"; return the reason instead.
+		err = ctx.Err()
+		if errors.Is(err, context.DeadlineExceeded) {
+			err = fmt.Errorf("gpg timed out: %w", err)
+		}
+	}
 
 	return &stdout, &stderr, err
 }
@@ -105,8 +138,8 @@ func parseFingerprint(colonOutput string) (string, bool) {
 
 // gpgSign creates a detached signature of the data using the specified key.
 // Returns the armored detached signature.
-func gpgSign(data []byte, keyID GPGKeyID) ([]byte, error) {
-	stdout, stderr, err := runGPG(bytes.NewReader(data),
+func gpgSign(ctx context.Context, data []byte, keyID GPGKeyID) ([]byte, error) {
+	stdout, stderr, err := runGPG(ctx, bytes.NewReader(data),
 		"--detach-sign",
 		gpgOptArmor,
 		"--local-user", string(keyID),
@@ -120,8 +153,8 @@ func gpgSign(data []byte, keyID GPGKeyID) ([]byte, error) {
 
 // gpgExportPublicKey exports the public key for the specified key ID.
 // Returns the armored public key.
-func gpgExportPublicKey(keyID GPGKeyID) ([]byte, error) {
-	stdout, stderr, err := runGPG(nil,
+func gpgExportPublicKey(ctx context.Context, keyID GPGKeyID) ([]byte, error) {
+	stdout, stderr, err := runGPG(ctx, nil,
 		gpgArgs([]string{"--export", gpgOptArmor}, string(keyID))...,
 	)
 	if err != nil {
@@ -136,8 +169,8 @@ func gpgExportPublicKey(keyID GPGKeyID) ([]byte, error) {
 }
 
 // gpgGetKeyFingerprint gets the full fingerprint for a key ID.
-func gpgGetKeyFingerprint(keyID GPGKeyID) ([]byte, error) {
-	stdout, stderr, err := runGPG(nil,
+func gpgGetKeyFingerprint(ctx context.Context, keyID GPGKeyID) ([]byte, error) {
+	stdout, stderr, err := runGPG(ctx, nil,
 		gpgArgs([]string{"--with-colons", "--fingerprint"}, string(keyID))...,
 	)
 	if err != nil {
@@ -157,7 +190,7 @@ func gpgGetKeyFingerprint(keyID GPGKeyID) ([]byte, error) {
 // gpgExtractPubKeyFingerprint imports a public key into a temporary keyring
 // and extracts its fingerprint. This verifies the key is valid and returns
 // the actual fingerprint from the key material.
-func gpgExtractPubKeyFingerprint(pubKey []byte) (string, error) {
+func gpgExtractPubKeyFingerprint(ctx context.Context, pubKey []byte) (string, error) {
 	// Create temporary directory for GPG operations
 	tmpDir, err := os.MkdirTemp("", "mfer-gpg-fingerprint-*")
 	if err != nil {
@@ -181,7 +214,7 @@ func gpgExtractPubKeyFingerprint(pubKey []byte) (string, error) {
 	}
 
 	// Import the public key into the temporary keyring
-	_, importStderr, err := runGPG(nil,
+	_, importStderr, err := runGPG(ctx, nil,
 		gpgArgs([]string{gpgOptHomedir, tmpDir, "--import"}, pubKeyFile)...,
 	)
 	if err != nil {
@@ -191,7 +224,7 @@ func gpgExtractPubKeyFingerprint(pubKey []byte) (string, error) {
 	}
 
 	// List keys to get fingerprint
-	listStdout, listStderr, err := runGPG(nil,
+	listStdout, listStderr, err := runGPG(ctx, nil,
 		"--homedir", tmpDir,
 		"--with-colons",
 		"--fingerprint",
@@ -212,7 +245,7 @@ func gpgExtractPubKeyFingerprint(pubKey []byte) (string, error) {
 
 // gpgVerify verifies a detached signature against data using the provided public key.
 // It creates a temporary keyring to import the public key for verification.
-func gpgVerify(data, signature, pubKey []byte) error {
+func gpgVerify(ctx context.Context, data, signature, pubKey []byte) error {
 	// Create temporary directory for GPG operations
 	tmpDir, err := os.MkdirTemp("", "mfer-gpg-verify-*")
 	if err != nil {
@@ -252,7 +285,7 @@ func gpgVerify(data, signature, pubKey []byte) error {
 	}
 
 	// Import the public key into the temporary keyring
-	_, importStderr, err := runGPG(nil,
+	_, importStderr, err := runGPG(ctx, nil,
 		gpgArgs([]string{gpgOptHomedir, tmpDir, "--import"}, pubKeyFile)...,
 	)
 	if err != nil {
@@ -262,7 +295,7 @@ func gpgVerify(data, signature, pubKey []byte) error {
 	}
 
 	// Verify the signature
-	_, verifyStderr, err := runGPG(nil,
+	_, verifyStderr, err := runGPG(ctx, nil,
 		gpgArgs([]string{gpgOptHomedir, tmpDir, gpgOptVerify},
 			sigFile, dataFile)...,
 	)

mfer/gpg_test.go

@@ -4,11 +4,13 @@ package mfer
 import (
 	"bytes"
 	"context"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/spf13/afero"
 	"github.com/stretchr/testify/assert"
@@ -43,8 +45,11 @@ Expire-Date: 0
 	paramsFile := filepath.Join(gpgHome, "key-params")
 	require.NoError(t, os.WriteFile(paramsFile, []byte(keyParams), 0o600))
 
+	ctx, cancel := context.WithTimeout(context.Background(), gpgTimeout)
+	defer cancel()
+
 	//nolint:gosec // paramsFile is a test-controlled path inside t.TempDir()
-	cmd := exec.CommandContext(context.Background(), "gpg",
+	cmd := exec.CommandContext(ctx, "gpg",
 		"--batch", "--gen-key", paramsFile)
 
 	cmd.Env = append(os.Environ(), "GNUPGHOME="+gpgHome)
@@ -55,7 +60,7 @@ Expire-Date: 0
 	}
 
 	// Get the key fingerprint
-	cmd = exec.CommandContext(context.Background(), "gpg",
+	cmd = exec.CommandContext(ctx, "gpg",
 		"--list-keys", "--with-colons", "test@mfer.test")
 
 	cmd.Env = append(os.Environ(), "GNUPGHOME="+gpgHome)
@@ -90,7 +95,7 @@ func TestGPGSign(t *testing.T) {
 	t.Setenv("GNUPGHOME", gpgHome)
 
 	data := []byte("test data to sign")
-	sig, err := gpgSign(data, keyID)
+	sig, err := gpgSign(context.Background(), data, keyID)
 	require.NoError(t, err)
 	assert.NotEmpty(t, sig)
 	assert.Contains(t, string(sig), "-----BEGIN PGP SIGNATURE-----")
@@ -101,7 +106,7 @@ func TestGPGExportPublicKey(t *testing.T) {
 	keyID, gpgHome := testGPGEnv(t)
 	t.Setenv("GNUPGHOME", gpgHome)
 
-	pubKey, err := gpgExportPublicKey(keyID)
+	pubKey, err := gpgExportPublicKey(context.Background(), keyID)
 	require.NoError(t, err)
 	assert.NotEmpty(t, pubKey)
 	assert.Contains(t, string(pubKey), "-----BEGIN PGP PUBLIC KEY BLOCK-----")
@@ -112,7 +117,7 @@ func TestGPGGetKeyFingerprint(t *testing.T) {
 	keyID, gpgHome := testGPGEnv(t)
 	t.Setenv("GNUPGHOME", gpgHome)
 
-	fingerprint, err := gpgGetKeyFingerprint(keyID)
+	fingerprint, err := gpgGetKeyFingerprint(context.Background(), keyID)
 	require.NoError(t, err)
 	assert.NotEmpty(t, fingerprint)
 	// The fingerprint should be 40 hex chars
@@ -146,12 +151,12 @@ func TestGPGOptionLikeKeyIDIsNotAnOption(t *testing.T) {
 	_, gpgHome := testGPGEnv(t)
 	t.Setenv("GNUPGHOME", gpgHome)
 
-	pubKey, err := gpgExportPublicKey(GPGKeyID("--version"))
+	pubKey, err := gpgExportPublicKey(context.Background(), GPGKeyID("--version"))
 	require.Error(t, err)
 	require.ErrorIs(t, err, errGPGKeyNotFound)
 	assert.NotContains(t, string(pubKey), "gpg (GnuPG)")
 
-	fpr, err := gpgGetKeyFingerprint(GPGKeyID("--version"))
+	fpr, err := gpgGetKeyFingerprint(context.Background(), GPGKeyID("--version"))
 	require.Error(t, err)
 	assert.NotContains(t, string(fpr), "gpg (GnuPG)")
 }
@@ -162,7 +167,8 @@ func TestGPGSignInvalidKey(t *testing.T) {
 	t.Setenv("GNUPGHOME", gpgHome)
 
 	data := []byte("test data")
-	_, err := gpgSign(data, GPGKeyID("NONEXISTENT_KEY_ID_12345"))
+	_, err := gpgSign(context.Background(), data,
+		GPGKeyID("NONEXISTENT_KEY_ID_12345"))
 	assert.Error(t, err)
 }
 
@@ -185,7 +191,7 @@ func TestBuilderWithSigning(t *testing.T) {
 	// Build the manifest
 	var buf bytes.Buffer
 
-	err = b.Build(&buf)
+	err = b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Parse the manifest and verify signature fields are populated
@@ -251,14 +257,14 @@ func TestGPGVerify(t *testing.T) {
 	t.Setenv("GNUPGHOME", gpgHome)
 
 	data := []byte("test data to sign and verify")
-	sig, err := gpgSign(data, keyID)
+	sig, err := gpgSign(context.Background(), data, keyID)
 	require.NoError(t, err)
 
-	pubKey, err := gpgExportPublicKey(keyID)
+	pubKey, err := gpgExportPublicKey(context.Background(), keyID)
 	require.NoError(t, err)
 
 	// Verify the signature
-	err = gpgVerify(data, sig, pubKey)
+	err = gpgVerify(context.Background(), data, sig, pubKey)
 	require.NoError(t, err)
 }
 
@@ -267,15 +273,15 @@ func TestGPGVerifyInvalidSignature(t *testing.T) {
 	t.Setenv("GNUPGHOME", gpgHome)
 
 	data := []byte("test data to sign")
-	sig, err := gpgSign(data, keyID)
+	sig, err := gpgSign(context.Background(), data, keyID)
 	require.NoError(t, err)
 
-	pubKey, err := gpgExportPublicKey(keyID)
+	pubKey, err := gpgExportPublicKey(context.Background(), keyID)
 	require.NoError(t, err)
 
 	// Try to verify with different data - should fail
 	wrongData := []byte("different data")
-	err = gpgVerify(wrongData, sig, pubKey)
+	err = gpgVerify(context.Background(), wrongData, sig, pubKey)
 	assert.Error(t, err)
 }
 
@@ -284,12 +290,12 @@ func TestGPGVerifyBadPublicKey(t *testing.T) {
 	t.Setenv("GNUPGHOME", gpgHome)
 
 	data := []byte("test data")
-	sig, err := gpgSign(data, keyID)
+	sig, err := gpgSign(context.Background(), data, keyID)
 	require.NoError(t, err)
 
 	// Try to verify with invalid public key - should fail
 	badPubKey := []byte("not a valid public key")
-	err = gpgVerify(data, sig, badPubKey)
+	err = gpgVerify(context.Background(), data, sig, badPubKey)
 	assert.Error(t, err)
 }
 
@@ -312,7 +318,7 @@ func TestManifestSignatureVerification(t *testing.T) {
 	// Build the manifest
 	var buf bytes.Buffer
 
-	err = b.Build(&buf)
+	err = b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Parse the manifest - signature should be verified during load
@@ -341,7 +347,7 @@ func TestManifestTamperedSignatureFails(t *testing.T) {
 
 	var buf bytes.Buffer
 
-	err = b.Build(&buf)
+	err = b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Tamper with the signature by replacing some bytes
@@ -375,7 +381,7 @@ func TestBuilderWithoutSigning(t *testing.T) {
 	// Build the manifest
 	var buf bytes.Buffer
 
-	err = b.Build(&buf)
+	err = b.Build(context.Background(), &buf)
 	require.NoError(t, err)
 
 	// Parse the manifest and verify signature fields are empty
@@ -390,3 +396,62 @@ func TestBuilderWithoutSigning(t *testing.T) {
 	assert.Empty(t, manifest.pbOuter.GetSigningPubKey(),
 		"signing public key should be empty when not signing")
 }
+
+// fakeGPGPath writes script as an executable named gpg into a temporary
+// directory and returns a PATH value with that directory first.
+func fakeGPGPath(t *testing.T, script string) string {
+	t.Helper()
+
+	binDir := t.TempDir()
+	//nolint:gosec // G306: the fake gpg has to be executable
+	require.NoError(t, os.WriteFile(filepath.Join(binDir, "gpg"),
+		[]byte(script), 0o700))
+
+	return binDir + string(os.PathListSeparator) + os.Getenv("PATH")
+}
+
+// TestGPGTimeoutKillsGPG puts a fake gpg that never finishes first on
+// PATH and checks that a run past its deadline is killed and reported as
+// a timeout of the named operation, instead of hanging.
+func TestGPGTimeoutKillsGPG(t *testing.T) {
+	t.Setenv("PATH", fakeGPGPath(t, "#!/bin/sh\nexec sleep 10\n"))
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+
+	_, err := gpgSign(ctx, []byte("data"), GPGKeyID("any"))
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+	assert.Contains(t, err.Error(), "gpg sign failed: gpg timed out")
+}
+
+// TestGPGTimeoutWhenChildHoldsOutput uses a fake gpg that runs sleep as a
+// child instead of exec-ing it, the way a wrapper script around the real
+// gpg might. Killing the fake gpg leaves sleep holding its stdout and
+// stderr open; the call must still return shortly after the deadline
+// instead of waiting for sleep to exit.
+func TestGPGTimeoutWhenChildHoldsOutput(t *testing.T) {
+	t.Setenv("PATH", fakeGPGPath(t, "#!/bin/sh\nsleep 3\nexit\n"))
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+
+	start := time.Now()
+	_, err := gpgSign(ctx, []byte("data"), GPGKeyID("any"))
+	require.ErrorIs(t, err, context.DeadlineExceeded)
+	assert.Less(t, time.Since(start), 3*time.Second,
+		"the call waited for the child holding gpg's output to exit")
+}
+
+// TestBuildPassesContextToSigning checks that a caller can cancel the gpg
+// runs that sign a manifest through the context given to Build.
+func TestBuildPassesContextToSigning(t *testing.T) {
+	t.Parallel()
+
+	b := NewBuilder()
+	b.SetSigningOptions(&SigningOptions{KeyID: "any"})
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	require.ErrorIs(t, b.Build(ctx, io.Discard), context.Canceled)
+}

mfer/scanner.go

@@ -283,8 +283,7 @@ func (s *Scanner) ToManifest(
 	}
 
 	// Build and write manifest
-	//nolint:contextcheck // Build's GPG signing exec is not cancellable by design
-	return builder.Build(w)
+	return builder.Build(ctx, w)
 }
 
 // configureBuilder constructs a manifest builder configured from the

mfer/serialize.go

@@ -2,6 +2,7 @@ package mfer
 
 import (
 	"bytes"
+	"context"
 	"crypto/sha256"
 	"errors"
 	"fmt"
@@ -50,13 +51,13 @@ func newTimestampFromTime(t time.Time) *Timestamp {
 	}
 }
 
-func (m *manifest) generate() error {
+func (m *manifest) generate(ctx context.Context) error {
 	if m.pbInner == nil {
 		return errInnerNotSet
 	}
 
 	if m.pbOuter == nil {
-		e := m.generateOuter()
+		e := m.generateOuter(ctx)
 		if e != nil {
 			return e
 		}
@@ -77,7 +78,7 @@ func (m *manifest) generate() error {
 	return nil
 }
 
-func (m *manifest) generateOuter() error {
+func (m *manifest) generateOuter(ctx context.Context) error {
 	if m.pbInner == nil {
 		return errInternal
 	}
@@ -135,7 +136,7 @@ func (m *manifest) generateOuter() error {
 
 	// Sign the manifest if signing options are provided
 	if m.signingOptions != nil && m.signingOptions.KeyID != "" {
-		return m.signOuter()
+		return m.signOuter(ctx)
 	}
 
 	return nil
@@ -143,27 +144,27 @@ func (m *manifest) generateOuter() error {
 
 // signOuter signs the outer message with the configured GPG key and
 // embeds the signature, signer fingerprint, and public key.
-func (m *manifest) signOuter() error {
+func (m *manifest) signOuter(ctx context.Context) error {
 	sigString, err := m.signatureString()
 	if err != nil {
 		return fmt.Errorf("failed to generate signature string: %w", err)
 	}
 
-	sig, err := gpgSign([]byte(sigString), m.signingOptions.KeyID)
+	sig, err := gpgSign(ctx, []byte(sigString), m.signingOptions.KeyID)
 	if err != nil {
 		return fmt.Errorf("failed to sign manifest: %w", err)
 	}
 
 	m.pbOuter.Signature = sig
 
-	fingerprint, err := gpgGetKeyFingerprint(m.signingOptions.KeyID)
+	fingerprint, err := gpgGetKeyFingerprint(ctx, m.signingOptions.KeyID)
 	if err != nil {
 		return fmt.Errorf("failed to get key fingerprint: %w", err)
 	}
 
 	m.pbOuter.Signer = fingerprint
 
-	pubKey, err := gpgExportPublicKey(m.signingOptions.KeyID)
+	pubKey, err := gpgExportPublicKey(ctx, m.signingOptions.KeyID)
 	if err != nil {
 		return fmt.Errorf("failed to export public key: %w", err)
 	}