fix(build): re-include local bin overrides in the generated .dockerignore

[initializ-mk]

Problem

The generated .dockerignore unconditionally excludes .local-bins/, but a build with local bin overrides (--local-bin name=/path or bin_overrides.<name>.local) generates a Dockerfile that COPYs each override straight from the build context:

COPY .local-bins/forge /usr/local/bin/forge

docker build then fails:

ERROR [3/6] COPY .local-bins/forge /usr/local/bin/forge
CopyIgnoredFile: Attempting to Copy file ".local-bins/forge" that is excluded by .dockerignore (line 21)
failed to compute cache key: "/.local-bins/forge": not found

Hit in a real CI pipeline (Buildkite, demo-weather agent) using --local-bin forge=… — the documented path for baking a vnext-prerelease forge runtime into the image, since the snapshot binary's self-reported version is not a real release tag the Dockerfile could pin.

Fix

Append a !.local-bins/<name> negation per override after the blanket .local-bins/ exclusion — dockerignore is last-match-wins, so each override re-enters the context while any unrelated stash content stays excluded. The config+CLI override union is extracted into localBins(), shared with copyLocalBins so the two can't drift.

No behavior change for builds without local bin overrides (pinned by a new test).

Testing

• TestDockerignore_ReincludesLocalBinOverrides — negations present for both config (bin_overrides) and CLI (--local-bin) overrides, ordered after the exclusion
• TestDockerignore_NoLocalBins_KeepsPlainExclusion — no negations in the default path
• Full forge-cli suite passes; golangci-lint clean; gofmt clean

[initializ-mk]

Review: re-include local bin overrides in .dockerignore

The fix is correct, well-scoped, and well-tested — it unblocks a real CI failure. One defense-in-depth finding on unvalidated bin-override names (pre-existing, but this PR extends it to a new sink). Not blocking; can be a fast follow-up. CI fully green.

The fix is right ✅

• dockerignore semantics: !.local-bins/<name> negations appended after the blanket .local-bins/ exclusion — last-match-wins re-enters each override while unrelated stash content stays excluded.
• Deterministic: names sorted → reproducible .dockerignore (cache-stable).
• localBins() extraction shared between copyLocalBins and the dockerignore generation prevents drift — the right refactor, since a mismatch would reintroduce this exact bug.
• No default-path change (len(bins) > 0 gate), pinned by TestDockerignore_NoLocalBins_KeepsPlainExclusion; the re-inclusion test checks config + CLI overrides AND the ordering-after-exclusion invariant. Good coverage.

Finding — Low/Medium (defense-in-depth): bin-override names are unvalidated

name reaches three sinks unsanitized, and nothing validates its charset (parseLocalBins checks the path, not the name; ValidateForgeConfig has no bin_overrides check):

1. fs write — dst := filepath.Join(localBinsDir, name) in copyLocalBins; a ../ name traverses outside .local-bins/ (pre-existing).
2. Dockerfile — COPY .local-bins/<name> /usr/local/bin/<name> (pre-existing).
3. .dockerignore — the new !.local-bins/<name> line (see inline) — a newline injects arbitrary dockerignore patterns; a glob re-includes the whole stash.

Threat model: for local forge build on your own agent this is self-inflicted → a non-issue. But Forge's CI/BYO story includes a platform building untrusted BYO forge.yaml, where a crafted bin_overrides.<name> becomes an injection vector across all three sinks. Impact is bounded (traversal → build host's output area; dockerignore re-includes limited to context contents), but a real hygiene gap once configs aren't self-authored.

Recommendation: validate the name against a strict binary-name pattern (e.g. ^[a-zA-Z0-9_.-]{1,64}$) in both parseLocalBins (CLI) and ValidateForgeConfig (bin_overrides) — closes all three sinks at the source. Since the more dangerous sinks (fs traversal, COPY) already exist on main, fair to land this dockerignore fix now and validate names in a fast follow-up.

The dockerignore fix is sound and merge-ready on its own.

[initializ-mk]

Defense-in-depth (Low/Medium): name is written here unsanitized. It's fully user-controlled (bin_overrides.<name> in forge.yaml, or --local-bin name=…) and nothing validates its charset — parseLocalBins checks only the path, and ValidateForgeConfig has no bin_overrides check. A newline in a name injects arbitrary .dockerignore lines here (e.g. !../secrets or !. re-including unintended build-context paths); a glob like * re-includes the whole .local-bins/ stash you just excluded.

This PR adds .dockerignore as a third sink alongside the pre-existing ones — copyLocalBins's filepath.Join(localBinsDir, name) (a ../ name traverses outside .local-bins/) and the Dockerfile COPY .local-bins/<name> /usr/local/bin/<name>. For local self-authored builds this is self-inflicted, but for a platform building untrusted BYO forge.yaml it's a real injection vector.

Closing it at the source — validate the name against ^[a-zA-Z0-9_.-]{1,64}$ in parseLocalBins and ValidateForgeConfig — fixes all three sinks at once. Pre-existing on main, so it needn't block this fix; worth a fast follow-up (a bin_overrides name is a binary basename, so the strict pattern costs nothing).