feat(#2097): migrate Augment onto EoS declarative adapter + settings.json MCP companion (ADR-1239)

Fold augment's runtime-literal conversion branches onto descriptor-driven
hostBehaviors and delete dead code:
- Site A (_applyRuntimeRewrites case 'augment'): the 4 ~/.augment dot-dir
  regexes now derive from getDirName('augment') via escapeRegExp (byte-
  identical; getDirName('augment')==='.augment') — no runtime literal.
- Site B (applyRuntimeContentRewritesForCommandsInPlace): the
  `if (runtime==='augment')` markdown-converter branch now reads
  runtime.hostBehaviors.commandBodyConverter and dispatches through a local
  COMMAND_BODY_CONVERTERS map (degrade-closed on unknown/absent name).
- Deleted dead `claudeToAugmentTools` map (zero refs; orphaned by ADR-1508
  single-sourcing) and the unreachable `else if (isAugment)` agent-conversion
  branch (augment ∈ _DESCRIPTOR_AGENTS_RUNTIMES → gated out upstream).
- Incidental orphan cleanup (no-defer): removed the equally-unreachable
  `else if (isTrae)` agent-conversion arm left behind by trae's already-merged
  migration #2094 (trae ∈ _DESCRIPTOR_AGENTS_RUNTIMES, same upstream gate).
  copilot/windsurf/codebuddy arms are removed by their own pending migrations.

UPGRADE 3 (transport:mcp): register the GSD companion MCP server in Augment's
settings.json under mcpServers.gsd (Augment hosts MCP in settings.json, not a
standalone file). mergeGsdMcpServerIntoSettings mutates the in-memory settings
object finishInstall already writes (gated on hostBehaviors.mcpCompanion===
'settings-json'); non-destructive + idempotent; symmetric uninstall removal.
settings.json is golden-excluded, so no golden change. UPGRADE 1 (named/
background dispatch) + UPGRADE 2 (settings-json hook bus, Claude dialect)
were already live in production — this adds tests exercising both.

Golden: byte-identical for all 16 runtimes (folds preserve regex behavior;
MCP lives in golden-excluded settings.json) — verified by a real double-install
tree diff. Tests: declarative-reference-augment (adapter/axes/fail-closed/
undocumented-sub-axes + source-grep guard scoped to conversion-logic branches)
+ augment-upgrades (dispatch negotiation, hook-bus live install, MCP add/
idempotent/preserve/uninstall). Matrix + connect-gsd-mcp-server + a stale
install-on-your-runtime hook-ownership claim corrected; changeset (Changed).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/reference/host-integration-capability-matrix.md

@@ -334,6 +334,35 @@ Documentation gaps:
 - dispatch.nested
 - dispatch.maxDepth
 
+**EoS migration status (#2097):** Folded onto descriptor-driven dispatch.
+Augment already installed through the declarative adapter (nested-skill
+artifact layout, `settings-json` hook surface, Claude hook event dialect), but
+carried two remaining runtime-literal branches in
+`src/runtime-artifact-conversion.cts`: the 4 `~/.augment`/`$HOME/.augment`
+dot-dir rewrites in `_applyRuntimeRewrites`'s `case 'augment':` block are now
+built from `getDirName('augment')` (dirName-derived, byte-identical) instead
+of a hardcoded `.augment` literal, and the
+`applyRuntimeContentRewritesForCommandsInPlace` command-body conversion
+dispatch now reads `runtime.hostBehaviors.commandBodyConverter`
+(`"convertClaudeToAugmentMarkdown"`) instead of a hardcoded
+`runtime === 'augment'` branch. Two dead-code sites were also removed from
+`bin/install.js`: the orphaned `claudeToAugmentTools` map (superseded by the
+single-sourced converters per ADR-1508 / #1675) and the unreachable
+`else if (isAugment) { content = convertClaudeAgentToAugmentAgent(content); }`
+inline agent-conversion branch (augment has been on the descriptor-agents path
+since `_DESCRIPTOR_AGENTS_RUNTIMES` was introduced, making that `if`/`else if`
+arm dead). **UPGRADE 3 — MCP companion config**
+(`mergeGsdMcpServerIntoSettings`) registers the `gsd` MCP server directly
+inside the same `settings.json` `mcpServers` block GSD's own hook
+registration already writes (Augment hosts MCP in `settings.json`, unlike
+Antigravity's standalone `mcp_config.json`) — non-destructively preserving
+any other user-configured `mcpServers` entries; uninstall removes only the
+GSD-owned `gsd` entry. `settings.json` is golden-excluded
+(`HOOK_CONFIG_FILES`), so this upgrade produces no golden fixture change.
+Source-grep guard + fail-closed negotiation coverage is in
+`tests/declarative-reference-augment.test.cjs`; the dispatch/hook-bus/MCP
+upgrade coverage is in `tests/augment-upgrades.test.cjs`.
+
 ---
 
 ## qwen