docs(#2869): record ADR-2866 install-surface resolution (#3265)

Phase 0 of epic #2866. Records the decision that the install pipeline
resolves surface identity — (runtime × scope × trigger) — as a value
instead of implying it from destination paths.

The ADR makes four things explicit:

- Amends ADR-3660 (placement -> placement + trigger resolution) and says
  why placement-only stopped paying: the /gsd-<name> trigger two
  artifacts collide on is not a value anywhere, so #2218 cannot be
  stated by any module or test.
- Adds one axis to ADR-1016's deliberately-closed descriptor vocabulary
  (host trigger precedence), required-with-default so ADR-894's
  additive-only stability contract holds.
- Records the @-include constraint (expands ~, does NOT expand env
  vars, no conditional syntax) as the reason #2218 triage option 1 is
  REFUTED rather than merely deprioritized.
- Notes the non-conflicts: completes ADR-58 rather than revising it,
  and preserves ADR-1508's dependency direction.

ADR-3660 and ADR-1016 each gain the reciprocal Amended by back-link,
matching the corpus convention ADR-2782 already set on ADR-1016. Each
states that the decision is recorded now while the modules change at
Phase 2 (#2871), so no reader is told a widening has already shipped.

Also corrects CONTEXT.md's Installer Module entry: bin/install.js is
hand-authored, not generated. ADR-1508 states this verbatim and no
build step emits it; the stale annotation invites contributors to look
for a generator that does not exist.

Docs-only. Verified via the remote runner.

Closes #2869

Co-authored-by: sim <sim@local>

docs/adr/README.md

@@ -181,6 +181,7 @@ These govern the system as it stands. Cite these.
 | [ADR-2629](2629-phase-effort-estimation-calibration.md) | Phase effort is estimated against a calibrated smart-zone budget, not a static heuristic | Accepted | — |
 | [ADR-2719](2719-emitted-artifact-attribution.md) | Emitted-artifact attribution — replace the committed parity fixtures with a computed conservation law | Accepted | — |
 | [ADR-2782](2782-reviewer-lane-capability-surface.md) | Reviewer Lane — the cross-AI reviewer handoff becomes a declared capability surface | Accepted | — |
+| [ADR-2866](2866-install-surface-resolution.md) | Install-surface resolution — the install pipeline resolves `(runtime × scope × trigger)` as a value | Accepted | — |
 | [ADR-2966](2966-loop-qa-walk.md) | Test the five-step loop as a continuous walk, not isolated points | Accepted | — |
 | [ADR-3180](3180-planning-semantic-model-single-owner.md) | Planning Semantic Model — Single Owner per Derivation | Accepted | — |
 | [ADR-3212](3212-lexical-seam-consolidation.md) | The Lexical Seam — Safe Pattern Construction, Line-Terminator Normalization, and Tokenizer-First Stateful Grammars | Accepted | — |