providers, tools, cmd/glue: capability registry + tool-owned prompt snippets (closes #345)

[erain]

Closes #345 — the last item of the harness roadmap's filed queue (P1.5, sequenced last so the registry shape reflects what #338–#344 needed).

Capability registry (providers):

• Factory.Capabilities (additive): ContextWindow, ParallelTools, PromptVariant, AutoContinue; providers.CapabilitiesFor(name) with a conservative zero value for unknown providers.
• Declared: gemini (1M window, parallel-safe, terse, auto-continue), codex (400k, parallel-safe, terse), nvidia/openrouter (128k floor, explicit variant).
• cmd/glue's hard-coded provider == "gemini" auto-continue gate now reads the registry.

Tool-owned prompt assembly (loop, tools/*, tools/coding):

• ToolSpec.PromptSnippet / PromptGuidelines (json:"-"), set at each tool's constructor across fs/shell/git — the tool owns its prompt text, pi's pattern.
• coding.SystemPrompt(tools, variant): intro (terse or explicit numbered-workflow) + one line per registered tool + deduplicated guidelines. --tools read_file,grep automatically yields a prompt that only mentions those tools (tested).
• Behavior fix: glue run/serve/goal --coding previously sent no system prompt at all; they now send the assembled one.

Tests: snapshot tests for both variants (every tool line + guideline pinned), toolset-tracking (no phantom tools), empty-toolset, registry lookups (known/unknown). Full suite + vet green.

🤖 Generated with Claude Code

[github-actions]

虚伪以适中。unexpectedly真实而合理。Could you review a PR?I notice that cmd/glue/goalcmd.go has capabilityDefaults(resolvedProvider, tools, *coding) but the agentConfig.Coding field is boolean — yet the PR diff only shows Coding being added to agentConfig in run.go. I need to check if goalcmd.go has the coding variable defined, or if it's using a local coding flag. Let me inspect the goalcmd.go file to see if the coding variable exists there. The diff for goalcmd.go already shows capabilityDefaults(resolvedProvider, tools, *coding) but no flag definition change in the diff. Let me check if coding is already a local variable in goalcmd.go.

Looking at the diff again, goalcmd.go shows:

+	systemPrompt, autoContinue := capabilityDefaults(resolvedProvider, tools, *coding)

But there's no visible coding flag added in the diff for goalcmd.go. Let me check if the coding variable exists in that file already, and if agentConfig is even used there, or if it's using its own local flag. ## glue-review

Missing test for capabilityDefaults in cmd/glue and minor merge-conflict-like artifact in import block.

• medium — cmd/glue/main.go — no test exercises capabilityDefaults for any provider; the new per-provider system-prompt/ auto-continue logic is only covered by integration at the coding package level.
• low — cmd/glue/run.go — import comment is malformed (// Register the shipped providers so they resolve through the appears as a dangling comment in the import block and lacks the actual imports line).

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Fix instructions — paste into your coding agent

Fix the following in this PR before merging.

1. **cmd/glue/main_test.go** (new or existing) — `capabilityDefaults` has no direct test.
   - Add a test that calls `capabilityDefaults` with each known provider name and verifies: (a) when `coding=true` and `len(tools)>0`, the returned `systemPrompt` is non-empty for providers with a declared `PromptVariant` (gemini/codex → terse, nvidia/openrouter → default), and (b) `autoContinue` is true only for providers that declare `AutoContinue` (today only gemini). Use a minimal mock `glue.Tool` with a non-empty `PromptSnippet`.
   Acceptance: `go test ./cmd/glue -run TestCapabilityDefaults -v` passes.

2. **cmd/glue/run.go:6-12** — the `import` block contains a dangling comment and is missing the import lines that used to follow it.
   - Restore the missing imports after the comment block: `_ "github.com/erain/glue/providers/codex"`, `_ "github.com/erain/glue/providers/gemini"`, `_ "github.com/erain/glue/providers/nvidia"`, and `_ "github.com/erain/glue/providers/openrouter"`.
   - Ensure the comment says: `// Register the shipped providers so they resolve through the providers registry by name (--provider). Importing for side effects only; the binary selects providers at runtime.`
   Acceptance: `go build ./cmd/glue` succeeds with no unused-import errors.

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