feat(server): allow integrations to raise the response cap per-tool

[daltoniam]

Summary

• Adds PerToolMaxResponseBytesIntegration, an optional interface that lets an integration raise the 50KB default response cap for a single tool without loosening the safety net for the rest of its surface. The integration-wide MaxResponseBytesIntegration override remains the fallback when no per-tool value is declared.
• Threads the tool name through both responseLimitFor callsites (server.handleExecute and ProjectRouter.makeExecuteHandler) so the new interface runs on both the standard and project-scoped paths.
• Puts the interface to use on github_get_pull_diff (raw unified diff, no projection/pagination knob, 1MB cap). The agents PR review flow has been hitting "Response exceeded 50KB" for normal-sized PRs (a 21-file/5k-line PR is ~200KB); this unblocks it without touching the other 195 GitHub tools.

Motivation

The model kept calling github_get_pull_diff, Switchboard kept rejecting the 193KB diff response, and the agent ran out of recovery moves. Switchboard already had a per-integration cap override (Confluence at 256KB), but raising the cap integration-wide for GitHub would weaken the safety net for the other 195 tools that should stay compact. The per-tool override targets the one tool that legitimately needs more headroom.

Test plan

• gofmt -w . && go vet ./...
• go build ./...
• go test ./... -count=1
• golangci-lint run (0 issues)
• New unit tests pin both callsites: TestHandleExecute_PerToolCap{Honored,DoesNotLeakToOtherTools,WinsOverIntegrationCap} on the server path; TestProjectRouter_ExecutePerToolCap on the project router path; TestMaxResponseBytesForTool on the GitHub integration.

💘 Generated with Crush

[acmacalister]

Clean PR — builds, tests pass (race detector clean), lint 0 issues. The layered priority logic in responseLimitFor is exactly right, the compile-time assertion in the GitHub adapter is a nice safety net, and the test matrix covers all three meaningful scenarios (honored, isolation, wins-over-integration-cap) on both the main and project-router paths. LGTM.