Expose audited hardcoded tunables as plugin config

The audit swept every packages/*/* plugin for the new AGENTS.md
convention (no hardcoded tunables in plugins) and exposes each finding
as a defaulted, validated Config field. Defaults are the previously
hardcoded values throughout, so no deployment or golden changes.

- tool-fs (had NO Config): readLimit, readMaxLineLength, readMaxBytes,
  readStreamMinSize. The caps thread through ReadToolCaps/ReadWindow —
  read-render already documented that the consumer applies the caps, so
  they become explicit per-request fields.
- tool-web: searchMaxResults (WEB_SEARCH_MAX_RESULTS stays as the
  schemastery default). Also fixes the stale GREP_LIMIT references in
  search.ts and the web-capability-seam RFC (no such constant exists).
- bash-local: graceMs (SIGTERM->SIGKILL escalation grace). The
  RunInternals.graceMs test seam is gone: graceMs is now a required
  SpawnSpec field filled from config, so tests exercise the real
  config path and the defaults live in exactly one place.
- subagent-acp: disposeEofGraceMs / disposeGraceMs. The AcpRunSpec
  fields become required for the same one-defaulting-layer reason.
- session-persistence-sqlite: journalMode ('wal' default; the
  rollback-journal modes serve filesystems where WAL's shared-memory
  files do not work, e.g. network mounts).
- hooks-claude + hooks-codex: stderrSummaryMaxChars for the persisted
  hook/result stderr summary. The duplicated summarize() helpers merge
  into hook-protocol's summarizeStderr(stderr, maxChars), beside the
  HookResultRecord field it feeds, with the bound parameterized the
  same way runHook's defaultTimeoutMs already is.
- compact-basic: charsPerToken for the token estimator (default 4, the
  English-text heuristic; CJK-heavy deployments need ~1-2 or compaction
  fires far too late). Also corrects the BasicCompactService class doc,
  which claimed defaults the required-field config never had.
- fs-local: deletes the dead STREAM_MIN_SIZE constant and the dead
  FsIoInternals.streamMinSize seam — the read-routing bound lives in
  the consumer (tool-fs), where it is now config. This is item 1 of
  the proposed prune-write-only-fs-surface RFC, annotated accordingly.

Every new field gets range validation (following the existing
assertPositiveFinite pattern), a README row, and tests covering the
configured behavior, the schema default, and load-time rejection.

packages/web/tool-web/tests/tool-web.spec.ts

@@ -15,6 +15,7 @@ import {
   presentFetchCall,
   renderBody,
   htmlToMarkdown,
+  WEB_SEARCH_MAX_RESULTS,
 } from '@deepseek-ai/dsh-tool-web'
 
 const available: WebProviderStatus = { available: true }
@@ -279,3 +280,48 @@ describe('tool-web execution through the real registry', () => {
     await fiber.dispose()
   })
 })
+
+describe('searchMaxResults is plugin config', () => {
+  it('forwards the default cap to the seam when unconfigured', async () => {
+    const seen: { maxResults?: number | undefined } = {}
+    const provider: WebSearchProvider = {
+      id: 'stub-search',
+      status: () => available,
+      search: (request) => { seen.maxResults = request.maxResults; return Promise.resolve({ providerId: 'stub-search', query: 'q', sources: [], truncated: false }) },
+    }
+    const { fiber, call } = await mountTools({ webConfig: { searchProvider: 'stub-search' }, search: provider })
+    await call('web_search', { query: 'q' })
+    expect(seen.maxResults).toBe(WEB_SEARCH_MAX_RESULTS)
+    await fiber.dispose()
+  })
+
+  it('forwards a configured cap to the seam, which enforces it', async () => {
+    const sources = Array.from({ length: 5 }, (_, i) => ({ url: `https://s${i}.test` }))
+    const provider: WebSearchProvider = {
+      id: 'stub-search',
+      status: () => available,
+      search: request => Promise.resolve({ providerId: 'stub-search', query: request.query, sources, truncated: false }),
+    }
+    const { fiber, call } = await mountTools({ config: { searchMaxResults: 2 }, webConfig: { searchProvider: 'stub-search' }, search: provider })
+    const out = await call('web_search', { query: 'q' })
+    expect(out.isError).toBe(false)
+    const body = out.content.map(b => b.text).join('')
+    expect(body).toContain('https://s1.test')
+    expect(body).not.toContain('https://s2.test')
+    expect(body).toContain('Showing the first 2 sources.')
+    await fiber.dispose()
+  })
+
+  it.each([
+    ['zero', 0],
+    ['negative', -3],
+    ['fractional', 1.5],
+  ])('rejects a %s searchMaxResults at load', async (_label, value) => {
+    const ctx = new Context()
+    await ctx.plugin(SystemPrompt)
+    await ctx.plugin(ToolRegistry)
+    await ctx.plugin(WebService, {})
+    await expect(ctx.plugin(ToolWeb, { searchMaxResults: value }))
+      .rejects.toThrow(/tool-web: searchMaxResults must be a positive integer/)
+  })
+})