fix(skill): provide directory context in system prompt and slash-command paths

[shyuan]

Issue for this PR

Closes #33786

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The skill's base directory was missing or URL-encoded in two code paths, preventing the agent from resolving bundled resources (references/, scripts/) relative to the skill install directory.

1. System prompt <available_skills> URL-encoded <location>

Skill.fmt() in packages/opencode/src/skill/index.ts used pathToFileURL(skill.location).href for the <location> field. This is the same bug #33580 fixed in the skill tool's base directory, but this second occurrence in the system prompt was missed. When a skill lives in a git-tagged plugin cache dir (e.g. ...git#v1.3.0), the agent sees ...git%23v1.3.0 and cannot use the path. Changed to emit skill.location directly.

2. Slash-command skills had no directory context

When a user types /skill-name, the skill is registered as a command (packages/opencode/src/command/index.ts) whose template returned only item.content — the raw SKILL.md body. Unlike the skill tool, there was no Base directory hint, so the agent had no way to locate bundled files. Added the base directory + relative-path hint to the template, matching the skill tool's output format.

How did you verify your code works?

• bun test test/skill/skill.test.ts — 16 tests pass
• bun test test/tool/skill.test.ts — 2 tests pass
• Confirmed both code paths by reading the source: Skill.fmt() now emits a plain path, and skill-as-command templates now include the base directory line

Screenshots / recordings

N/A — no UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search, I found one potentially related PR:

Related PR:

• #29429 - fix(opencode): load full skill context for slash skills

  This PR also addresses providing context for slash skills. While fix(opencode): load full skill context for slash skills #29429 may have addressed loading full skill context, the current PR fix(skill): provide directory context in system prompt and slash-command paths #33787 fixes a specific bug where the directory context was either missing (in slash-command paths) or URL-encoded (in the system prompt's <available_skills> section), preventing proper resource resolution for bundled skill files.

These appear to be complementary fixes for different aspects of skill context handling rather than direct duplicates.

No other duplicate PRs found addressing the same specific issues of URL-encoded <location> in Skill.fmt() or the missing base directory hint in slash-command templates.

[shyuan]

Re: the bot's note about #29429

Worth clarifying since the bot framed them as "complementary" — for bug 2 (slash-command skills lacking directory context), #29429 and this PR actually overlap on the same lines in command/index.ts, so they're alternative solutions rather than complementary:

• fix(opencode): load full skill context for slash skills #29429 sets the slash template to "" and routes source === "skill" commands through skill.execute(...) in session/prompt.ts, producing the full skill context (including the ripgrep-sampled <skill_files> listing).
• This PR keeps it lightweight: it just appends the Base directory hint to the template, matching the skill tool's wording but without the file listing.

I went with the lightweight approach because it resolves the reported symptom (agent can't locate bundled references//scripts/) with a minimal, self-contained change and no new execution path. If the maintainers prefer the richer file-listing behavior from #29429, bug 2 here can be dropped to avoid the conflict — but bug 1 (the pathToFileURL URL-encoding of <location> in Skill.fmt()) is independent and not touched by #29429, so that part stands on its own regardless.

[shyuan]

Superseded by #34052 (fix(opencode): preserve skill resource paths), which already landed on dev and fixes the same two code paths this PR targeted:

• skill/index.ts: fix(opencode): preserve skill resource paths #34052 uses escapeHtml(skill.location) for <location>, which fixes the URL-encoding issue and properly XML-escapes values like <built-in> — strictly better than this PR's plain skill.location.
• command/index.ts: fix(opencode): preserve skill resource paths #34052 adds the same base-directory hint for slash-command skills.

The only remaining unique change here was a doc-string typo (reference/ → references/) in tool/skill.ts, which has no functional impact. Closing in favor of #34052; the typo can be picked up in an unrelated change if needed.